apvp,1. "By default, a tmpfs partition has its maximum size set to half your total RAM, but this can be customized. Note that the actual memory/swap consumption depends on how much you fill it up, as tmpfs partitions do not consume any memory until it is actually needed." See: https://wiki.archlinux.org/index.php/Fstab#tmpfs
2. Exactly.
Also, I recommend using reiserfs for /var. Read ArchWiki pages for a lot of useful info. I never used Ubuntu Wiki, have no clue of what is there.
