I would like to put on a set of classic style 20's to fill the wheel well better and would like to snug it down with out loosing factory ride too much. What size offset rims, tire size, and lower all 4 or just rear spring kit to go with ?

 

20 x 8 wheels with the offset of +35 to +42mm for starters, rim wise. 235/235r20 tire size and any brand lowering springs you like. I have goldlines pn mine and I think they are just great. However, as far as the springs go I have nothing to compare them to as I install mine with 21 miles on the HHR.

 

Good avdise all around there. However, I think, if you want more of a stock ride, do what harleysshhr said but go with just the Goldline rear leveling springs. I've had both leveling and lowering springs. The lowering springs are a stiffer ride than the leveling springs. The coils are a smaller diameter but wound tighter to acheive the lower stance and still handle the load of the car weight.
FYI, 42mm is stock offset.