I'm not sure 20" would hurt your truck. Don't see why it would, other than they're maybe heavier. Sure you'd be fine though. I think it looks better with smaller rim/ bigger tire. Not into the big rims look personally
I got my rims and tires for about 1600. U should go to americas tire co. and see what they can do for u. If u plan in lifting it, u should wait so u can put the bigger tires