Aaron,

For the rear track most people always run max width which is 172mm.
The front track is mostly fixed. When you get the proper bearings in the wheels chances are at most you can add one small shim but really there is not alot to alter in the front without some modification which if you are running a 1/12th for the first time sticking to stock is probably best.

Getting back to the rear width its commonly believed that running max width in the back gives the most stable rear. Running a little narrower gives more grip. Same basically with the front.

As for the bearings some rims require flanged some flangeless, you should maybe just consider having a set of each.

Hopes this helps

Steve