RE: throttle channel use mandatory?
You can use another channel, such as ch5 which is often used for flaps.
If it is electric powered, just make good and darn sure you first check the motor direction, end points and slider direction without a propeller attached. Also, with our use of the sticks firmly ingrained in our muscle memory, it will take a while to get used to the fact that the throttle stick is no longer the throttle stick. Easy to get crossed up on those first few flights.
You are going to find that with anything more than a basic set-up you're going to be extremely limited with what you can do with 6 channels.