What is the correct offset and tire size for 18's
 

I've decided to go with 18's on my car. The only size the wheels come in that I'm buying are 18x7.5 with a 45+ offset. Is this gonna fit properly on a Max? I'll be putting H&R sports on it as well.

Now as for tire size...

235/40/18 or 225/40/18

Adam has 225/40/18 on 18's. Will the 235/40/18's look to big? I've seen some cars that look like freakin' ballon tires on them. I kind of want to avoid that.