Wheels for 2003 Silverado

Hello

I'm in the process of purchasing a set of 20 in wheels for my 2003 Silverado. I'm new to the this larger size. I would like to have an agressive look. My questions are. Should I get 8.5 or 10??? What size of tires should I put on???? What about the backspacing??? What is the best place to buy wheels and tires??? I'll be lowering the rear end to make it level. Any information will be very helpful.

Thanks
Raul
2003 Silverado
Las Vegas, NV

Personally I would go with the 8.5" width. That's just my own preference, but the 10" would give you the more agressive look you after, althought they may stick out from under the fenders but I don't think that should happen. I would go with a 275/45/20 or 285/50/20.