Only reason to drop to 18s would be for tracking the car and those wheels are much heavier than stock so that would be a double no-no. my suggestion, if your looking for a way to make your car look better with minimal money. Instead of going with those TE37 copies, get 20mm/25mm spacers and Swift springs, and powder coat your wheels what ever color you were wanting. it will look better in my opinion and be more functional. and probably even save you some money.
but it is your car, so if you are selling your wheels for those. stay with 19s.