Want suggestions for best practices piping to potable expansion tank

I've got an Amtrol potable expansion tank installed circa 2001, when we had the lead service replaced and required back flow preventers installed. I suspect the potable tank has failed internally - it's suspended from threaded tee in 3/4" sweated copper running across ceiling as cold supply to water heater, and it sounds 'full' when I thump it. The water heater TPRV has burped and reseated a couple times - so something's clearly amiss. I plan to check my city water pressure with a gauge, shut down water heater, shut off incoming water supply, drop and drain the potable tank, check and recharge to same as city water pressure? slightly higher? - then reinstall if I don't hear hissing through a blown diaphragm, and replace if I suspect a problem. I know it's a heavy wet mess to take down an expansion tank, and I'm thinking of adding isolation valve between tank and cold water supply - then wondered if one valve is enough, or if I want one to leave on the water line, and another on the tank, and maybe a third on a bleeder tee.... am I overthinking this, or do any of you have an favored clever arrangement that makes servicing potable expansion tanks less of a dripping pouring nuisance?