We use both 2 channel and 16 channel radios from Motorola. The 2 channel are generally all you will ever need. This assumes you do not want to scan the SCCA or other track frequencies. Many radio shops will charge you for each channel programmed (not expensive). I think that you will be fine with 2 and maybe 3 authorized (FCC) frequencies. There is more to this than what I'm writing here. Another thought is to contact one of the Frequency Coordinator companies as they will do all of your paperwork and get the best choices for the tracks you are going to. This is the part few talk about-trust me it is very important to get each of the forms completed correctly and pay the fees in one shot.
Got Q's drop me an e-mail and I'll try to help.