depends what plane you are flying ... for me 9 - 10 is a necessary minimum. Here are some basic functions to keep mind of: ( of course some could be mixed with primary controls )

- throttle
- ailerons - elevator
- rudder
- flaps
- retracts
- brakes

that’s 7 right there ...


others you could use ..

- another aileron channel for crow mix ability
- separate nose steering channel
- airbrakes
- smoke
- aux turbine channel ( on some engines )
- canards ( on some types of airframes)
- tank/bomb drop
- the list goes on ......

Voy