I personally think 19" look best. For some reason, 20"s look a little bit too big for the car. Just my opinion though. Saying that, I love ATTAK Z's old konig afterburners in 20" but they were mainly black so didn't look too massive.
As for tyres, it all depends on your budget. It's a big jump from 19" to 20" in terms of cost, whereas 19" tyres aren't too different from 18". Most people here run Falken FK452s or Bridgestone Potenza RE050s. The best tyre if you have the money is the Michelin Pilot Sport PS2 though. That's pretty much all I'm going to say. If you talk too much about tyres on here someone usually kicks off and it ends in an epic battle between docwra and Ekona. Nobody likes it when that happens, but it does make for quite a good read.