You will not have any issues with ride quality or handling characteristics with the car. You might slightly feel the weight difference on acceleration and in turns but it will not affect anything with the car if you step up to a 20" wheel. I ran many different 20" widths and offsets with tires...
Depending on what you are lowered with yes. If you have a 1" drop you can do a 265/35 & 305/30. If you are lowered more you can do a 275/30 & 305/30 and go with a little bit of a wider tire up front. When I had my eibach sportlines with a 20x10 / 20x11 fitment i ran the 275/30 & 305/30 and it...
We call it the "Stillen Stunner"! This incredible red chrome wrapped Infiniti Q60 showcases all the Stillen bits including that sick prototype rear wing! Huge AP Racing Radi-Cal Brakes look perfect behind our 20" Vossen x Work VWS-1 wheels. Nitto Tires keep things planted and RS-R Suspension...