I have to agree with what a few of you said, "Trying to do too much" shouldn't be an issue here. Most of the main guys should get plenty of screentime in their own solo movies, so character development shouldn't be an issue. Favreau can focus on how the already-known characters relate to each other, as in LOTR.
(Emphasis on the SHOULD, notice I'm not saying "won't". Anything can happen.)