It appears that this coach was well maintained.
Yes, diesel repairs could be very expensive but I would think your expenses on this rig would be RV related rather than chassis related. I.e. Refrigerator, holding tank maintenance, etc.
There is a bit more maintenance on a diesel but not that much that makes it not doable.
I have read on the forums that many folks pay for service work so as not to have to deal with the larger quantity of oil found in diesels. To each their own.
Filters are filters. Diesel filters cost a little more but typically have a longer service life. Special installation procedure for fuel filters, maybe. But they all spin on and off. Most of the time easier to replace than on a car.
The worst thing for any RV is to let it sit in storage.
Good luck on your purchase and the countless family memories out on the road.