Sounds like you got the right idea. It depends on how many partitions and mount points you want, how much space Ubuntu will take, and how much space you want to save for programs that will be installed alongside the system and not in /home (although I don't think this could be much).
Many people like to have 3 or 4 partitions, / , /boot , /home , and swap. I read somewhere once that performance is supposed to be better if the swap partition is on a separate hard disk than the main operating system files. I never really seen any numbers on this though. Probably doesn't make that much of a difference, but its something you may want to think about.
I think a lot of its preference. Like you said, I would put /home on the 30Gig.
Ha! JimBass beat me to it!
Feeling dumb now.
Thats what I get for turning to the TV for 10 minutes