A Good City Adventure

I think it really needs to use the city, not just dungeons set in the city. Rival battling power groups are important - think Romeo & Juliet for a good model. You want duels in the street, roof-top assassins, bands of thugs lurking in dark alleys, that kind of thing. The city itself needs a starring role, so design with that in mind.

The first two books of "Curse of the Crimson Throne" do a good job of this, with lots happening in Korvosa itself.

Opposing groups can be:
Noble houses
Criminal gangs
Churches & cults
The City Guard
Rival sorcerers or mage guilds
Merchant guilds
Artisan guilds
Knightly orders
etc

Status Quo Sandboxing in 4e D&D

By default 4e is only really suitable for status-quo sandboxing within a demi-Tier. I am trying to stretch it to a Tier using Threats To The Nentir Vale, by Minionising many of the standard mook monsters in the level 4-7 range, eg level 6 brigand standard becomes a level 6 brigand minion, these are the most useable across the Tier. But a level 1 standard monster like an Iron Circle trooper needs to become a level 6 minion if he's to stay useable across Heroic Tier.

With giving minions 1/4 hp too, so far this seems to be working really well - I can use the same level 6, 18-21 hit point minion now with PCs at level 2-3, and at level 6, and even at level 10 with enough of them & keeping PC magic gear in the 1-10 range.
Level 11+ it'll break down though, so that's when I plan to transition to a mix of Domain Level play and high level questing, I have King of the Trollhaunt Warrens for that.

OD&D Quest Awards for 'Palaces & Princesses' Play

For the kind of "Palaces & Princesses" feel 2e AD&D was going for, I kinda think they would have been better off dropping monster & gold XP both and go for some kind of abstract Quest Award type XP system where you get say 1/10 of a typical level's advancement per significant achievement, or around 1/5 of a level per play session. At least as an option. They'd have needed a 9 or 10 level table of awards for achievements, much like the Monster Level I-X system, but I think it could have worked well for that edition. Something like:

Quest XP Awards per PC
Level      Major   Minor 
I                  250        50
II                500      100
III             1000      200
IV             2000      500
V              4000      800
VII           8000     1600
VIII        12000     2400
IX          16000     3200
X           20000     4000

The Best Online Tools for 5e

My main online tools are
http://rpgtinker.com/ - 5e NPCs
http://redkatart.com/dnd5tools/ - 5e Treasure Generator
http://donjon.bin.sh/fantasy/random/ - generates generic fantasy encounters, NPCs, worlds and planes - pretty much everything, really.

Together with http://www.5esrd.com/ that's pretty well enough to run a campaign!

5e Primeval Thule Class System

While some study for years to master the arts of magic, the path of the Warlock is temptingly quick and easy...

Starting Classes
Barbarian
Fighter
Monk
Rogue
Rogue
Warlock - Infernal or Old One

Eldritch Knight & Arcane Trickster
In order to become an Eldritch Knight, Arcane Trickster or other caster subclass the PC must already have the Ritual Caster (Wizard) feat. The quickest way to do this is to be a Variant Human with the Feat at 1st level.
Exception: High Elves have magic in the blood. They may become an Eldritch Knight or Arcane Trickster even without the Ritual Caster feat.

Wizard
To become a true Wizard the PC must first have 3 levels in a caster subclass such as Eldritch Knight. This means the effective maximum 'true wizard' level is 15.

Example: Bob wants to become a Wizard.
At 1st level he is a Human Fighter with the Ritual Caster (Wizard) feat. He could also have been a High Elf.
At 3rd level he becomes an Eldritch Knight.
At 6th level he can multiclass and become a Fighter (EK)-5/Wizard-1.

Is XP an Illusion?

From http://www.enworld.org/forum/showthread.php?555579-XP-is-a-major-weapon-in-the-DM-arsenal&p=7136463&viewfull=1#post7136463

I found running Classic D&D I could just hand out an amount of XP at the end of the session that felt right and that fitted roughly with the game's guidance of ca 5 sessions to level. I didn't need to do any calculating, just decide "This was a small/medium/big session" - and it seems to have all the positive benefits that use of XP gives over milestone/ad hoc levelling. Players get to write it down. They see how close they are to next level. They see a connection between achievement & reward.

This works equally well in 5e; the DMG even provides a handy table. Just hand out eg 1/5 or 2/5 the XP-to-Level for a typical session, then adjust up and down. Or go to a flat 20 XP to level and then give out 3, 5, 7 etc XP per typical session. 20 is a good number because you can give 1 XP per minor achievement & 2 XP per major achievement across the session, 1 XP per hour played, etc.

Resting in 5e

Looking at pacing, I'm looking at going over to the DMG 'gritty' rest variant where a Short Rest is overnight, and a Long Rest is 1 week. Not to screw with the players  :twisted: , but to give a better cadence to the passage of time, closer to real life (and game time pass at a rate closer to real time), so that eg typically a week passes between dungeon expeditions just as a week passes between game sessions. I think with having converted most Short Rest powers to x3 per Long Rest, this still allows 'nova-ing' within a single dungeon expedition or fight.
I would also have an overnight Short Rest recover 1 hp per level, and 1 level of Exhaustion in natural healing. Also a 7 day Long Rest would now recover all hit dice, not just half-rounded-down.

It does mean that LR abilities like Rages and high level Spell slots may be more at risk of running out if used liberally, eg using Rage just to get Advantage on an Athletics check may be a bad idea. My thinking is to trial this over the next few sessions and make sure it works ok and doesn't screw over any particular PCs.

NPC Demographics

Adventurers - I rarely have this as a recognised profession IMCs, so no % of the population are recognised Adventurers.

Classed NPCs - in games which give NPCs classes, such as my Classic D&D Mystara campaign, I'll tend to use Gygax's standard that 1% of the population have classes and are capable of advancement. Other, static, NPCs are statted as appropriate, so eg in Classic trained soldiers are typically at least Fighter 1/1 hit dice, those being functionally identical concepts.

Spellcasters - In my Wilderlands game you typically see one Cleric type NPC per few hundred of the population, something under 0.5% but above 0.1%. Wizard type NPCs are much rarer, one in a thousand or less. A village of 400 might or might not have a priest with Clerical spellcasting, if not they probably have a ritualist priest with no combat casting.
My Golarion (Paizo's world) 5e campaign probably has a similar number of Clerical casters & somewhat higher numbers for arcanists.
Not sure about my Classic Mystara setting, but same sort of ballpark. Only the Alphatians field actual units of spellcasters, the (eg) Heldannic Knights field units of Fighters with Clerical support, at most roughly 1 Cleric per 10 Fighters in their case, & more like 1 per 100 for most armies.

Combatants - Wilderlands uses 25% combatant (2 hd+ in 5e, 1hd/Ftr-1 in Classic). When I ran Gygax's Yggsburgh setting in 1e AD&D I used his DMG numbers - 20% combatant, 10% in prime condition (hp 4+) and suitable as men-at-arms.

Ranking - My Yggsburgh game also used EGG's mercenary level distribution, with Ftr 2-3 lieutenants & Ftr 5-8 captains  as indicative of power level for mid-rank and powerful NPCs. Conversely my Mystara Classic game sees the Heldannic Knights field entire squadrons of elite Ftr-7 knights, and the King of Ostland's 20 'Brothers' were statted as Ftr-15 accompanying King Hord Darkeye Ftr-28 per the Northern Reaches GAZ, which says 1% of the population are Ftr-11+!

From http://www.dragonsfoot.org/forums/viewtopic.php?f=11&t=12309&p=1847970#p1847970