Hi and welcome, Rob!
Stick to 18"s if you intend to do a lot of track work or want ultimate handling, 20"s if you're looking for bling but the best compromise for looks and handling has to be 19"s. Most people go for a staggered combo such as 8.5/9.5, 9/10, or 9.5/10.5 front/rear.
Design is obviously personal taste and budget is down to you but finding a lighter wheel will pay dividends with the handling.