in practically all states, a vehicle that is licensed as a motor home has to have one or more of the following: permanent cooking facilities, sleeping facilities or lav.
i don't think seats will matter, but i haven't checked the internet to see what michigan says, but i am pretty sure it wont be too far off if this. it doesnt mean that they have to be actually permanent.... if an inside inspection is required there, all they will look at is to see if there is a bed, or a stove and maybe a tiny apt frig... i have licensed conversions in 5 diff states, and never have i had anyone check inside.
what you gotta do is call up or send someone over to a dmv that you are not going to take it to and ask them what the rules are, but they are probably online as well.
most all inspections will be for mechanical... ie headlights, muffler, wipers, and stuff like tires, although most motorhomes do not have the same level scrutiny on the tires that your over the road ones get.. cause here in oregon we now only get 3 blemishes on our tractors... where as on my bus half the tires wouldn't pass.
and, its a short bus, so maybe they go by regular car standards instead of the heavy truck ones.
as far as seating.. i dont imagine there is a problem as long as they are bolted down, and the seat belt mounts are in the proper positions..
i think you have less to worry about than you think...