Current summer setup is 18x8 +35 w 225/40 (& RS-R Sports-i coils). Pic for reference of the look.
But if you gonna keep it in stock suspension, I'm talking about stock struts, sway, alignment then prob 17's (17x7.5~8.5) w 215/45 or 225/45 is ideal. 18's doesn't look bad, but it will loose lil bit of "fun" factor. Of course that vary w how grippy is the tires is.
Til when you know what you really want from this car, I would recommend avoid spending extra $ buying wider wheels and tires.
That's just my 2 yen.