When I speak about maintenance, there are really four categories (in my mind).
!) Required such as fluids, lube, and etc. that are on a fairly set schedule.
2) Optional such as tires, cleaning/waxing and the like.
3) Unscheduled repairs such as repairing leaking hydraulic hoses, AC, appliances and that sort of thing. Some are urgent some can be delayed to a more convenient time.
4) Upgrades which are totally optional which have included new front TV and cabinents, refig upgrade to residential, and etc.
For required maintenance I change oil and lube chassis every 2 years but I have 36 qts so I can go longer than a coach with 20 qts. Tranny every 4 years (transynd), coolant (ELC) every 4 years. For this I budget about $500.00/year and that's about right.
The optional category is another $500.00 or so per year. Tires are an erratic expanse and I budget those about a year or two in advance of implementation. This year I bought two new 12RX22.5 Hankook tires for $1,100 for the front and move the old front to the tag. Next year I might buy 4 new for the drive axle, than in another four years two new fronts and move those to the the tag.
Unscheduled is...well just that. Sometimes it's high and some years nothing.
Upgrades are where I seem to spend the most $$$.
As far as the DIYI, I don't do much of anything but write the checks.
Don't know if this helps you or not but it works for me.