You have lot of things to consider.
First if you want to spend money and LOT of your time for interior remodeling, you have to make sure you have good base.
No matter how much remodeling you do to school bus, it is still going to be a school bus.
Coaches like Prevost, MCI, Airstream, Eagle, Bart are getting remodeled forever as even 50 years old Airstream trailer is stronger than factory new wood and particle board trailer.
Check how much you can buy replacement cabinets for.
Almost anything in RV is custom and that does not come cheap.