Hi Lia, and welcome.
No doubt some of our more technical members will be along in due course with their wisdom, but personally when I had a van of that age I tended to follow the old "if it ain't broke, don't fix it" principle. Beyond the usual vehicle checks (oil, water, tyres, brake linings etc), as long as things were working I left them alone.
However it's probably wise to let qualified people look over your gas and mains systems from time to time for peace of mind.
I believe there's a "Haynes" manual for motorhomes in general. I've not seen one, but their car manuals are excellent so that may help.