First, of all starting with just a chassis ( or do you mean complete chassis) and buying parts
Separately will cost way more then buying a kit

Second ,if you want to do organized racing go to the track , see what classes they run and build a car to what you want to run

Third, Classes are usually built using lipo batteries , sensored brushless motors . Like 25.5 for VTA, 21.5 for GT 17.5 for TC.

Fourth, If you dont have a radio dont automatically buy a single model radio because if you like RC racing ,all you have to buy is reciever to add a second model . Only buy a 2.4ghz radio because at many tracks 27 and 75 mhz radios are not allowed .