Man this really needs to be broken down into segments that you intend to do.
Modular Pawn for the most part is what your talking about, figure out how to do this and your 80% of the way there.
IE skeleton - Character - Break Up Points laid out throughout all versions - Weight painting - getting the replication or display of different meshes at runtime.
If you can get through that then the rest of what you want to do will be fairly simple. Look up modular pawn in these forums or UE3 and start there.