33 should be around the same size. why not go 35 if you don't mind me asking...they'll fit with your level and new wheels.
with regards to the wheel size..it's personal preference.
20x9 will have more rim less tire sidewall
18x9 will have less rim more tire sidewall than the 20" wheels. I personally like more tire less rim so I dropped to 17" wheels. Some people say that's the "old school way" that new school is a lot of rim. But for goin offroad and all I prefer smaller rims and a lot of tire.
Main benefit to dropping diameter..is you save a good chunk of change. My exact set up now in a 20" diameter would have cost me almost $1000 more... and i still have the same over all 35" in the end..just smaller rims.
JVC Arsenal KD, Bilstein 5100 adjustables [maxed], aFe Stage 2 Air Intake, Superchips 3865, Husky Floor Mats, Saddleman Camo Seat Covers, Flowmaster 40 Series Muffler SI/DO, 20 % Tint. 35x12.5x17 Federal Couragia M/T, 17x8.5 VTEC Warlord wheels, -12mm offest.