Need a couple Wheel/tire combo's answered

Hi,

About to order a set of wheels, and was wondering what kind of backspacing i should be looking to get. Wheels will be Crager S/S. 15x7 is about the widest a fully stock dart gt can handle, right?

http://www.summitracing.com/parts/CRR-61754/
is what im looking at. I think it will be a fine match. I'd just like some input/backup.

I was also thinking of going 225/60/15 on all 4's, will this be a wise choice or should i go smaller. Car will be a Sunday driver, will occasionally drive it to work. Maybe more.

next few questions..... while im at it, Im going to replace the left hand threaded lug studs, can those be found on summit?
7/16" is the lug size?