If I restore my iPhone, what will back up?

I have 3.5 gigs of "other" memory, and I just went through my Messages, Contacts, Email, Safari, etc and basically cleared everything. I don't think 15 open conversations and 128 contacts, 30 emails and 0 safari usage should take up 3.5 gigs.

I read that I should restore my phone to reset the "other" usage. I'm going to, but when I back it up, I want to make sure not EVERYTHING goes onto my phone when I restore it. I have contacts, music, etc that I don't want on my phone. I just spent 2 hours clearing it out, how can I make sure when I restore the info that ONLY the stuff currently on it goes back on?

Only the stuff that you have checked in the backup will go on your iPhone.

Everything is backed up.