This is a somewhat smaller scale campaign idea than the other two, and really only applies to Heroic levels. At this point I almost see that as a benefit and this is probably the one most likely to get played in the next few months.
I LOVED Pool of Radiance when it came out in 1989. I spent a huge amount of time playing it on my Commodore 64 as did my friends. It centered around a ruined city in the Forgotten Realms that was being slowly reclaimed by the inhabitants. Players made up a party and worked through the different sections of the city clearing out the monsters which were all conveniently level appropriate with the weaker ones nearer to the civillized section and the stronger ones deeper in the ruins. There were also side trips outside the city to a huge graveyard, a lizardman lair, and a mad wizard's pyramid. The computer game was awesome for the time and it came with a great little background book that really captured the favor of the area. TSR also published a 1st ed module version of this campaign titled Ruins of Adventure. It should have been the Realms version of Keep on the Borderlands but it failed badly and has largely been forgotten. Except by me.
So to start a new campaign of D&D I like to have a safe base area, some dungeons close at hand, some options for local countryside wandering, and some political or religious things going on to give the more roleplay oriented types something to do between dungeon crawls. This adventure fits that perfectly. Plus many of the adventures in the ruins involve more than just a frontal assault - many are centered around sneaking into something or talking your way past guards and many areas have some kind of guardians that can be reasoned with so there is more here than just carnage. There is plenty of violence though, and every kind of monster from kobolds to hill giants and dragons, lots of the D&D staples. Re reading the module made me realize it has a lot of good ideas just some poor presentation and limited monster stats - perfect for a conversion to another edition.,particularly this edition if its proponents are to be believed.
Classes: Anything goes. I'll pick up the Realms guides for 4th and however they've worked them into the Realms works for me.
Races: Same thing here - there's a book that explains all this so no extra effort for me.
The Gods - again, there's a whole book for this so that's what I will use.
Environment - it's a single large ruined city on the coast of the Moonsea and some of the surrounding features. Perfect - I don't have to build or convert a continent, just a one-page map.
Adventures - This is a fixed mission in some ways - reclaim the city! - but it's not a railroad, it's more of a sandbox. There's a big map and the players can approach it however they want. If your 2nd level band wanders into the hill giant lair then a lot of bad stuff is going to happen. Add in some factional differences on the town council and everyone should be able to find some interesting things to do.
Phlan and the Moonsea was the first area of the Reams I was exposed to and I really liked it. I have run almost no D&D in the Realms, spending most of my time there as a player as my friend ran the Realms like I run Greyhawk. But things change, so maybe it's time I tried it.
Note on the 100 year jump: I know the 4th edition realms is set 100 years after the old realms stuff but I don't think it matters. Phlan was ruined once and now it's ruined again sometime during that 100 year gap. My players didn't play through this module then (other than the computer game) so they have no investment in the original situation. Heck, maybe Tyranthraxus survived last time and has returned to finish what he started 100 years ago - either way it doesn't matter and doesn't cause any continuity problems with my game.
Expanding and improving this adventure should occupy my campaign through the Heroic levels and set them up as well known heroes around the Moonsea and major players in Phlan itself. At that point we could decide to continue, switch to something else, or start a new 4th edition game using the lessons learned here to improve the next one, maybe one of my other campaign ideas. Whichever way I think this is the best for a DM & players new to 4th edition and it's probably the way I will go.