Question about Halo 3

Ok, so I bought a 360 a while ago (bought core i didnt know it didnt come with hardrive) and i just left it too rot. So now Im planing to get a hardrive, live and halo 3. The question i have is that will there be like ways to make clans? Because i havnt played halo 2 online and also will there be any like BIG levels like BIG BIG levels were you NEED warthogs to move unless you want to walk for a long time.

halo 2 had full clan support, so im thinking they'll bring it into halo 3 also.

some levels should be big but you can most probably walk through it all.