#1. low latency make you feel "connected" to your vehicle.
#2. Channel 1=steering, Channel 2= throttle, Channel 3&4 are typically aux or battery input for receiver, transponder, 6.0 volt fan(8volt fan will spin slow)
#3. Buying top dollar will definitely pay off depending how serious your plan on racing. will have feature like telemetry(which i don't use but some do). Higher end radios will tend to have lower latency
#4. Sanwa/Airtronics, KoPropo, Futaba