Turbo787

Hello guys and gals...I got this 97 with 18s. Haven't even looked at the tire sizes either. The wheels are radd wheels model rd3's. So I'm getting a good deal on some pinacle wheels...20" tires are 245/35/20. I'm about to go get them tomorrow but I have no idea of what the offsets are or qhat should be. This is a rent a wheel cwnter...and thw guy says it qill fit my car. Any input will be great...they have another set w/o tires for about the same price of $600 that are 18"s...I don't know what to do...I already gave the deposit but I don't know if I should do these 20s or try to get the 18s? I've read threads on these wheel sizes and offsets but nothing on 4th gens... Thanks and hope someone can give some needed advice...