Thank you for the reply and info. From your post and the links you provided, it seems my system should have a 4GB swap partition (and considerably less would be OK, since it's primarily just a file server, I don't foresee it using anywhere near all its RAM at the same time very often--if ever).
I'm still not sure what to think about the other partitions (/var/spool, /tmp, etc.). I'm assuming it became unnecessary to have them separately partitioned during one of the upgrades, 9 to 10 or 10 to 11...but I haven't found any documentation about it yet, and I'd feel better if I knew for sure. If anyone can tell me or point me in the right direction, feel free to message/email me through the forum.
I did find answers to some of my other questions, though, so I'm posting them here so I can mark the thread as solved and maybe help someone else looking for the same info.
"Initially I included a /home partition of 20 GB, but when I did that it said the rest of the drive was "unusable". (???)"That happened because I made the mistake of setting /home to be a primary partition, making it my 4th primary partition on the drive. I didn't realize you're limited to 4 primary partitions or 3 primary + 1 extended.
"I read somewhere in these forums that once you install a GUI on server it basically is no different from desktop...is that true?"I found confirmation that--as of the 12.04 release--the only real difference between desktop and server versions is the presence or absence of the GUI/desktop environment:
"The amd64 -generic and -server kernel flavors have been merged into a single -generic kernel flavor for Ubuntu 12.04. Given the few differences that existed between the two flavors, it only made sense to merge the two and reduce the overall maintenance burden over the life of this LTS release."