61 stuff
I agree totally with everything Outwest said.
I would only add to your question regarding s/e engagments.
I have done this literally thousands of times. Start one engine (we used to alternate days), bring the Ng up 2% (if I recall correctly), smoothly release the rotor brake and Bob's your uncle. When the transmission is warm enough, bring the Nr up to 100%, then start and engage the 2nd engine. FYI, we NEVER had any unusual input wear doing this in many, many thousands of hours. Cheers, J.