a couple of questions concerning wheels

I just got my brand new 2006 Mustang v6 two days ago. Now I was looking for 20" wheels and I used to own a BMW but I don't know the bolt pattern for the wheels i'm looking for for the Mustang. And also if I put 20's whats the widest I can go in the rear without rubbing or anything? Would you guys have any suggestions for some 5 spoke rims with a deep lip in the back? Thank you for all your help.

and also i am dropping the car about an inch with the eibach springs would i still be able to fit 20's? and also how wide of tires would i be able to fit in the back? thanx a mill...