You will find loads of 1:18 models on ebay or try model shops like modelzone.Its fairly easy modding them,i started about 3 years ago & found the more i did the more little 'tricks' you pick up,like what will & won't work etc.Wheels are pretty easy to change,some makes screw on & others push on.All i can say is keep reading the threads here & ask as many questions as all the lads here are helpfull.
Good luck