So is a 4th channel necessary?
4pv or pls?

For electric rc cars a 4th channel is totally optional. With a 3ch RX you can power your ESC, Servo and an extra cooling fan for the motor or run a transponder. Although I believe a motor fan and a transponder can just use the same 3rd channel with a splitter cable.

Don't forget the battery port. The 3 channel receivers don't need a splitter to do both a fan and transponder.

I have a 3PV and 4PLS, but I'd say go for the 4PV if you plan on racing regularly.

The 3PV is great and has all the basic features that you could need, but lacks some more high-level adjustments such as servo return speed, has no timer function, no adjustability of the trigger or wheel position or tension. It is light and reasonably tough with a more basic menu system.

The 4PLS has all those extra features but is an older radio. The exposed folding antenna is a definite downside. Being able to adjust the trigger position, brake stop, trigger and steering tension is a big plus.

The 4PV is the newest Furaba radio and seems the best of both worlds- the newer replacement for the 4PLS. Whatever you get, look for the packages that come with the 'e' variant receivers if you'd like to do without antennas on the receiver.