I’m gearing up to run a D&D (Basic) or C&C campaign. This will probably run from about 1-8 level with a very modest level progression. I’m concentrating most of my effort on the back stories of the individual PCs and how they tie together.
Start with B2 (Keep in the Borderlands). You can tie any personalities and backgrounds in that you like, you can include whatever level of story you want in the keep. Remember, the focus of the module isn't the caves of chaos (even though thats the series of adventures), the focus of the module is the keep as an isolated community.
From there, for 'character' building I'd go with either B3 (Palace of the Silver Princess) or B4 (The Lost City), or even both. B3 (green cover, not the earlier version that was canned for being rubbish and which is now free as a PDF) is a lovely old fashioned 'rescue the princess' tale, its a well crafted and challenging module. B4 is Moldvay at his best, its a cool and cooky little module introducing a whole lost civilisation, an adventure where simply attacking things to get their treasure won't work.
That, together with your own additions, should see you through basic, and on to expert level.
X1 (Isle of Dread) probably isn't your cup of tea, from what you describe, but think more along the lines of running it like 'Lost'. The characters become stranded on this wierd island full of dinosaurs, to escape they have to work out what the heck thats all about. Its very much a wandering in the wilderness module, but with some work from the DM it becomes a treasure.
X2 (Castle Amber) is rather reminiscent of B4; same AUTHOR, again a very eccentric place. But of all of the X series, its the most D&D'ish.
Then for your purposes I'd go with X3, Curse of Xanathon. A city based adventure, with so many potential plot hooks and so much potential for character development, I'd say its the most useful of the X series for you.
From there... Well, X4 and X5 have great breadth of story and huge scope, but they're whole campaign type stuff. Not 'traditional' adventures. So I'd be tempted to go a little further out; once the characters are established, once they have a name for themselves within their setting, once they know who they are and what they are about, how about throwing I6 (Ravenloft) at them?
(EDITED to remove silly typo)