Manors & Dominions

I'll use the lowest listed 1e PHB rate of 5 sp/month as a default, with a Fighter of level 5-8 as ruler or steward, or a level 8 Cleric Patriarch, able to raise 6sp/month, about the OD&D level at 10 sp per gp.  Other rates as below.

1e AD&D uses monthly rates:
Fighter Dominion 7 sp/month Presumed default. This seems an appropriate rate for Paladins also, and possibly Rangers, if Aragorn is an example.
Clerical Dominion 9 sp/month Presumably includes tithes, so we can see that the Church may claim up to 2sp/month/person above the default rate.
Magic-User Dominion 5 sp/month Magic-Users apparently make poor rulers, having "many other demands on their time". This seems an appropriate income rate for other classes without specific rulership skill, such as Druids, Thieves & Assassins.
A kindly GM may allow the weaker rulership classes to employ a Steward, typically a Fighter type of level 5-8, who can raise taxes at the default rate of 6 sp/month, or 7 sp/month if the Steward is a Fighter type of level 9+. 9 sp/month should be reserved for theocratic dominons.
Note that subsistence income and minimal average GDP per person, including the non-productive, is 1 sp/day, or 30 sp/month. A typical 5 person household produces GDP of 150 sp/month.

New Manors
Initially attract freeholders on a manor equal to 'Max Henchmen' score x10 and if there's plenty of land grow as per table below. Of course diplomacy and conquest can enable rapid growth...
For random potential areas optionally roll 3d4 for the likely gp/year reflecting resources; Fighter Lords add +2 to the roll. 10gp/year assumes a near optimum environment.

Lord's CHA: Initial Freeholders (Manor)
3-4:  10; Growth -3%
5-6: 20; Growth -2%
7-8: 30; Growth -1%
9-11: 40; Growth +0%
12-13: 50; Growth +0%
14: 60; Growth +0.5%
15: 70; Growth +1.5%
16: 80; Growth +2%
17: 100; Growth +3%
18: 150; Growth +4%
19: 200; Growth +5%
A typical manor in settled farmlands is 640 acres, or 1 square mile. Maximum manor size in borderlands is roughly 2 miles diameter (one 2 mile hex), or just over 3 square miles, of which no more than 1 square mile is likely farmland. Exceptions apply to rulers of exceptional charisma - see below. Otherwise new manors must be created to administer the growing population.

Manor Current Population & Base Growth Rate (annual)
Under 20       +30%
20                 +25%
40                 +20%
60                 +15%
80                 +10%
100                 +5%
125                 +4%
150                 +3%
200                 +2%
300                 +1% requires 1.5 square miles farmland
400                 +0% " 2 sq m"
500                  -1% " 2.5 sq m"
600                  -2% " 3 sq m"
700                  -3% " 3.5 sq m"
800                  -4% " 4 sq m"
900+                -5% " 4.5 sq m"

A sub-infeudinated manor must have a lord or thane, preferably a henchman/retainer of the higher lord.

Resource Investment
For every 200gp spent on resource development in a month, a manor will attract 1d10 more people. Growth limits still apply.

Typical Domain Costs
A typical domain has gross income of 10gp/person/year and expenses of 75% of income, leaving a net income of 2.5gp/person/year.
Garrison: 20% (civilised)-30% (borderland)-40% (wilderness) of income (2gp-4gp/person/year)
Stronghold Upkeep: 5% of stronghold cost per year; typical strongholds cost = annual domain income x2 (civilised) x3 (borderland)  x4 (wilderness), so typically 10%-20% of income, 1-2gp/person/year
Salt Tax: 20% of gross income to higher lord, 2gp/person/year
Tithes: 0% (wilderness) -5% (borderland)-10% (civilised) of gross income to local churches/temples, 0gp-1gp/person/year
Festivals & Alms: 5% of income, 0.5gp/person/year

Urban Investment
It takes 1 year to create a new settlement at a suitable locale. Once created, the settlement maximum population figure is added to the maximum population figures above, so eg +30% annual growth requires a population fewer than 20 above the numbers below.
Investment  Additional Maximum Population
 10,000gp      +1000 Small Town
 25,000gp      +3000 Town
 75,000gp      +10000 Small City
200,000gp     +25000 Large City
625,000gp     +100000 Metropolis
2,500,000gp  +500000 Grand Metropolis

Growing a Manor (D&D & Mini Six)

The following rules are for D&D based systems. For Mini Six, replace Charisma with Charm - either rolled or taking 3 per Die for passive, so eg Charm 3d6+2 is a passive score of 11.

MANORS & DOMINIONS
OSRIC says high level Fighter Lords can extract 1gp/month per resident in a freehold; for general play I'm going with 10gp/year gross income for a typical borderland manor, which is the OD&D level. Initially attract I reckon freeholders on a manor equal to 'Max Henchmen' score x10 and if there's plenty of land grow quickly to around 100, slower thereafter. Of course diplomacy and conquest can enable rapid growth...

Lord's CHA: Initial Freeholders (Manor)
3-4:  10; Growth -3%
5-6: 20; Growth -2%
7-8: 30; Growth -1%
9-11: 40; Growth +0%
12-13: 50; Growth +0%
14: 60; Growth +0.5%
15: 70; Growth +1.5%
16: 80; Growth +2%
17: 100; Growth +3%
18: 150; Growth +4%
19+: 200; Growth +5%
A typical manor in settled farmlands is 640 acres, or 1 square mile. Maximum manor size in borderlands is roughly 2 miles diameter (one 2 mile hex), or just over 3 square miles, of which no more than 1 square mile is likely farmland.

Manor Current Population & Base Growth Rate (annual)
Under 20       +30%
20                  +25%
40                 +20%
60                 +15%
80                 +10%
100                 +5%
125                 +4%
150                 +3%
200                 +2%
300                 +1%
400                 +0%
500                  -1%
600                  -2%
700                  -3%
800                  -4%
900+                -5%

An OSR style XP chart for 5e D&D

Chart assumes standard monster XP, and XP for GP. Typical treasure should cap at Tier III level, ca 50,000gp/hoard, with Tier IV hoards being exceptional.

Level   XP
1           0
2      1000
3      3000
4      7000
5    15000
6    30000
7    60000
8  100000
9  150000
10 200000 'Name Level'
11 300000
+1 +100,0000 up to Level 20.

Magic Item Crafting
Rarity Minimum Level Time Cost
Common     4           2 days       200gp
Uncommon 8           7 days    1,000gp
Rare             12      31 days    5,000gp
Very Rare    16      92 days   25,000gp
Legendary   20   366 days  125,000gp

Youtube Channels for a Gamer/GM

I'd recommend watching Youtube videos on topics of interest, generally NOT gaming videos. I get more from:

Scholagladiatoria - weapons
Shadiversity - weapons, castles, dragons, etc etc
Lindybeige - history, weapons, culture, etc etc
PBS Spacetime - space, astrophysics
Science & Futurism with Isaac Arthur - what it says
John-Michael Godier - space
Dr Becky (admittedly her cuteness may be a big factor!)  - space
PBS Eons (though it's pretty lowbrow compared to Spacetime) - evolution/paleontology
Overly Sarcastic Productions - history, mythology, tropes

5e D&D House Rule - Bonus Skill Proficiencies for high INT

This is intended to deal with the 5e D&D 'INT as dump stat' issue.

Bonus Skill Proficiencies for high INT

A PC may begin play with a number of additional skill proficiencies from their class skill list equal to their INT bonus.

ie 12-13 = +1, 14-15 = +2, 16-17 = +3 etc. Multiclass characters choose from their starting class skill list.

If INT is raised during play, additional class skills up to the bonus limit may be learned using the Downtime rules in XGTE, ie 10 weeks - INT bonus per skill.
___

It's intentional that very high INT PCs may max out their class skill list, then being unable to take additional skills. It favours Wizards and to a lesser extent Rogues, which I think is ok.

Changing battlemat scale from 1 square = 5' to 3 squares = 10'

This has several advantages in terms of plausibility, mobility, et al.
Base sizes stay the same, so a 1" base figure still occupies 1 square, now about 3.3', or 1 meter. For diagonals, count 1 diagonal as 1 (3.3'), 2 diagonals as 3 (10').
5' reach = 2 squares
10' reach = 3 squares
15' reach = 5 squares
20' range = 6 squares
30' range = 9 squares
Now 8 characters with 5' reach can attack 1 from adjacent squares as before, but an additional 3x4=12 can attack from the second rank, the target benefitting from cover (+2 AC). Still, a mob becomes a lot scarier without having to worry about any in-and-out dance!

Running Paizo Adventure Paths, with reference to Skull & Shackles

From https://www.enworld.org/threads/your-experiences-with-skull-shackles.667617/#post-7820742

Clarity & Presentation - Paizo write primarily for the reader on their couch, not the GM at their table. The material tends to be incredibly verbose, and often irrelevant to at-table play. I have learned over time how to treat the material as a buffet and not be bound by what's written down. Eg you get a great NPC with a few paras of backstory, who is "Remains in room - fights to death - suicides if captured". The GM can delete that last bit, take her out of her room, create links with PC(s), make her a cool part of their own campaign.

Balance - S&S is known as ridiculously deadly in the early chapters. There is a general issue that 3e/PF balance is very tenuous even to start with, without author 'errors'. I had a lot of trouble running Curse of the Crimson Throne in PF, with the 2 min-maxed PCs slaughtering everything with ease while the 2 non-minmaxed PCs were nearly helpless. I solved this by converting APs over to 5e and making/converting my own stat blocks, with the PF ones as a guide. This is pretty easy, certainly easier than using a multi-column PF BBEG stat block as written.
Re S&S balance in particular, I don't have an issue with most merchant ships being so outmatched they surrender immediately; pirates don't go in for fair fights! I think the main thing there is that pirating per se shouldn't take up a large amount of play time. In Queen of the Black Coast REH covers three years of pirating in a couple lines. The interesting stuff happens when things go wrong.

Minigames - Paizo are legendarily awful at these. My best advice is to ignore whatever mechanics they give you and run the situation the same way you normally would. Eg instead of a chase sequence mini game in Curse of the Crimson Throne, I used a battlemat of rooftops, and the standard rules for jumping, climbing etc. Players will thank you for this, trust me! Likewise, instead of a doing an actual tarot/harrow-card reading & trying to interpret the results, just improvise some suitable NPC dialogue from the reader suitable to the PC - "I see the queen & crown - there are great things in your future, Lord Zerda! But the snake means you must be wary..."

Overall, I find the better PF APs (prob including S&S) to be well worth using, but sadly they are probably least suitable for a new GM, and most suited to a very experienced GM who knows when to ignore instruction. For a newbie GM I'd recommend something like Adventure Anthology #1 at basicfantasy.org