Ok so I'm trying to make sure I'm geared up properly for commuting and I have a couple of questions that searching didn't turn up exact answers for

Panniers, do I need two to balance out or will 1 suffice? I'll be commuting to school and work so I'll have to carry a little bit of stuff with me.

Secondly are there any panniers other than timbuk2 that come off and can be used as a backpack/messenger bag?

Third instead of a pannier could I just get a rack and strap my bag to that? I have both a timbuk2 med messenger and a chrome borris