When you register it you just register it like any other vehicle. There's an affidavit you can write up or print out that you can turn in to them that will change the title to "MH" if you want to.
Progressive commercial insurance will cover you, but DON'T apply online. Go to a physical insurance agent and set up a policy. Don't tell Progressive you're converting the bus, or they'll drop you. PROGRESSIVE DOES NOT INSURE CONVERTED SCHOOL BUSES.
Mine isn't "converted". Its a "mobile office".
Just make sure its a commercial policy for PRIVATE, personal use.