The Marais is a fantastic place, you're right near Place de la Bastille and Notre Dame (Île de la cité) and so much history. And the Seine.. I did Paris solo for a ten day trip, so it was quite nice walking to and sitting on the side of the seine with my (usually chocolate-based) dinner.
(loved being young and poor and living on baguettes and nutella).
It's also walkable to the Louvre, although the metro is really easy and if you get an all-day ticket, you generally end up using it..
If you're looking to hostel it, I'd really recommend MIJE (
http://www.mije.com). Clean rooms, quiet, in renovated historical houses in the Marais. It's got a lock-out period, and a curfew, but it really didn't bother me.
Also I bought guide books... but honestly, Wikipedia was the most helpful thing for actually deciding what arrondissement to stay in and such.