I'm looking for advise on servicing a leaky pressure relief valve at the tee from expansion tank and a ball valve near the expansion tank. Mostly I am concerned about shutting down the system there and draining those areas to make the replacements. Is this as simple as shutting off the well control, making the fixes and turning back on? Anything that needs to be done when turning the system back on? The system otherwise runs fine. Thanks!

Turn off the breaker, bleed off pressure, do work, turn system back on. While the system is down and drained, double check the pressure at the top of the pressure tank. It should be 2# below the cut in pressure for the system. So, for example, if the system is set to come on at 30#, set your tank to 28#.

What material are the pipes?
Copper? Galvanized? Follow jlisenbes advice and drain the system. If you're soldering copper ALL the water must be out of the pipes. No moisture at all. Good luck, Tom