Hi John,
These are all good questions. I use a SuperReg on my 50cc plane without a PowerExpander at the moment. You will need to make up some adapters to mate with the Deans Ultraplugs on the SuperReg and standard male R/C connectors on your receiver. I would recommend using two. You will need two Deans Ultra males and two male pigtails for the receiver.

I really do not know if the Triton can handle common ground but I think I may have heard it will NOT. I am not positive though.

You will need Deans Ultraplug females on your batteries.

Let me know if you have other questions.