Welcome! You've come to the right place. You certainly bought a large bus! First things I'd check are, Engine codes, King pins in the steering columns, ensure suspension is good,
If you have a good suspension and running engine without issues, get it inspected by a mechanic who knows buses well. Don't just go to any diesel mechanic, have them do a once over, even if you have to drive a distance to them, it'll be worth it. Have him do any little tunes, fixes he sees as becoming a problem soon. Much cheaper to head off issues now than when stranded on the road with a giant bus and paying a $4000 tow.
You can test king pins by pushing on the wheel, and see if there's any play pushing in and out, or if there's wear on the inside of the tire only. With so much weight you want to ensure all that is good to go.
Once all of that is in order, and you know it's good, then proceed with demolition and building up the inside of the cab.