Okey... So when I turn two knobs, only ONE works? Is this the same for the Mega? Sounds really limited?!
Literally this is true, a microprocessor can only ever do one thing at a time, but in practice it's not because things are happening at very fast speeds so it looks like it's all happening at the same time. So don't worry about that, it will work as you expect, turn a knob and the servo will follow, turn two knobs at once and both servos will follow their respective knobs (given the right software of course).
Just to confirm, can I have 8 analog inputs, and 38 digital inputs in one device with the Mega?
The docs state 54 IO pins, so 54 - 8 analogue = 46 left. So yes you will be OK.
Rob