[Theflexmaster]

-You can just merge all the files together to make a final scene, if thats what you mean. For the video post make sure you make the video post assigned by object id (so not everything gets the effect of the video post). Also for big scenes i'd recommend xrefing.

-If you mean skylight than it shouldn't be all that big of a addition to rendering. If you use the new daylight system in max 9, a lot of problems can occur with mr sky and mr sun. It can increase render time sometimes. Render time is based on the complexity of the scene for the most part.

-You could try bucket rendering with mental ray. This makes it so more than one computer works on a frame. Since mental ray is split into blocks when rendered, one computer can render a bucket (block) while another computer does another. This is limited to 8 processors (8 buckets) on one render, which sucks cause it'd be nice to have like 50 computers all rendering one frame at a time making like a super computer. Network rendering is a good alternative though, it splits up frames to each computer. Use backburner to do this, thats the only way i really know how to do it.

-I know there is a way to join clips through video post. I really don't know the process for it, alpha compositing maybe... i'm really not sure.