DX5e would be fine as a first transmitter on a budget. Fail-safing is done by the receiver so no need to worry about that. It has full dual stick controls: so Elevator, Aileron, Rudder and Throttle, as well as a single Auxiliary - So that is your 5 channels.

Its main draw back is that it has very limited mixing capabilities, it can only take 1 model at a time. You might have to cough up more money for a mixing unit that goes in the robot for example, and you would need to rebind and reset the fail safes every time you changed models.

Personally I'd look at a 2nd had DX6i, or a new DX6. Transmitters tend to hold their value better and the new DX6 is more robust. That said its a big price leap and keeping it simple first time is a good idea. Up to you, just some things to consider