Even on my fairly simple Waco Biplanes that does not have flaps, or retracts, I use the following:

2 Elevator
1 Rudder
1 tail wheel
1 adjustable horizontal stabilizer
1 throttle
2 aileron

That's 8. I have used 12 on some models, and could have use 14 if I had not used Y harnesses.

You might wonder why I use a seperate servo and channel for the rudder and tail wheel, but the tail wheel only travels 40% of the rudder movement.