1. Not possible right now since we can't import our own 3D models into the game. Sounds however shouldn't be any problem at all.
2. See point 1
3. That's rather easy to do. I think somebody is already doing it.
4. Hmmmm...that one could be complicated. How do you want the limit to work? Limit the amount of buildable cities and/or the amount of conquerable ones? All in all I doubt that this is possible.
5. Yay to the faction editor, texture mods and the ablitiy to scale units at will...so that one should be also pretty easy, however NO new 3D models here either.
6. Possible but would take damn long. New textures and tiles and objects all the way...nah.
7. Why would somebody want to do that?
8. James009D : So yeah there's the solution to that. 
9. Yeah...that's not hard either. Just add the unit_stat changes to the techs and there you go. Will kill your games balance however.