I would vary the sizes.. especially because you may not be able to fit the same size across the entire section (you want to cover as much as possible)
I bought a starter kit through Tami's website that was very helpful. It came with a polishing cloth, tweezers, glue and a pointer thing that you can dab in the glue.. Basically I made a blob of glue and just dipped the back of my crystals in it using the tweezers, but everyone seems to have their own method. Warning: it took hours but was well worth it.
I had tons of crystals left over and used them on my menus and place cards.
Tami was great about sending me actual pictures of the crystals I was interested in. It helped to really see the colors and sizes.