Well emails are VERY low in memory usage (as long as there's not large attachments), I don't know the exact kb, but I'm thinking less than a kb each (as some people seem to survive with 2mb..).
Facebook in 'standby' I'm unaware of however, I doubt it's much, it may even disconnect and reconnect somehow, but I really don't know. CALLING ALL TEKES! lol
I'm pretty sure the facwbook app only uses data when you get it to check peoples statuses or send a message.
It works by getting it's info from incoming messgaes so when it pops up saynig new messge etc it's not actually downloaded anything it's just read an email.
It's very hard to know what data your bb uses for anything, whilst emails use very little data anyway, blackberry have a very high compression on any data going through their servers which reduces the data amount even more.
I consider myself a fairly high user and use no where near your limits, so long as your not streaming video or music you should be fine.
If you want to save some more data usage then set your bb to use wife where ever possible this will save you a bit.
Posted from my CrackBerry at wapforums.crackberry.com
IMHO i don't even think the facebook app is necessary, well only to upload photos directly to facebook. i downloaded it, logged out and hid it so i wouldn't use it. i prefer the mobile website myself.
