Frame size is key, to some people. Example: I bought a walmart mountain bike Because it felt right~ It wasn't my "size" but it still felt right. I ride a 58 road bike, because it's my size and it fits right.

Did you ride it before you tore it apart? If your building a bike, it wasn't very smart to buy a frame without riding it first. Any rear rack will do, just research them and question what you need it for. It' up to you to question what you want to feel as you ride. Do you want handlebar higher then seat? Go faster or safer? What will you be using it for (commuting, duh) but for what?

I think more over on gearing, seat, tires, and ease of quick-on-the-side-of-the-road-tear-apart.