Isolating aux battery, etc

Howdy all,
I have a 2005 Ford E350 high top van, formally a paratransport van. I had the lift removed and would like to do the following with the auxiliary battery:
-install an isolator switch to so it won’t drain the engine battery when it’s used(if that’s a thing)
-install a battery level meter
-install a converter
-install usb and ac plugs
While I am very handy, this is out of my depth. Are these things possible/smart? What switch, meter, plugs do I need? Can a regular auto mechanic do this?
Thanks for all and any input.