I would get an ignition shut off - like the smart fly. One reason is for safety but they also have an LED which lets you know your ignition is on.

I have a DA-50R and I am very happy with it. I have never had a DLE, but I have had a cheaper engine and it ended up costing me way more than the price difference between it and a DA in deadstick crashes.

A lot of people buy those power expanders. I personally do not know if they are really necesssary. I guess you would need to add up the stall current of each servo then compare that to what the receiver can handle. I have a GP Ultimate Bipe and I just use the recommended servo size, which are not super high torque servos and I just plug them into the receiver.