ugh win8
as far as partitions go, i never really duel boot, just use vm's so leave at default partition settings as i usually(and quite quickly) break things and need to reload.
but as a rough guide try: du -hs /dir on an existing system to give you an idea of usage
/ : at a guess 50gb?
/swp: technically you don't really need to double your ram unless you have like less than 1gb, so 6gb is fine
/usr: depending on your usage, ~30gb for a desktop (this is at 1.7gb on this server)
/var: again depending on your usage, most of your logs will default to here, without logrotate can get quite large, especially if running servers, the server (18gb) is slightly skewed here as the backups are here
like i say this is pretty must guessing as i mostly use vm's and don't load the desktop enviroments