Welcome to The RV Forum, Becky!
I'd be more concerned about the wear and tear on the unit's interior (carpets, upholstery, appliances, etc.) if it's been lived in for long periods versus the lighter use given an RV that's only occupied a few weeks a year for vacations.
Also check carefully to make sure there aren't any critters or insects who may have decided to take up residence if it's in a wooded area.
5th wheels don't have much in the way of mechanical parts. Replace the tires, pack the wheel bearings, make sure the brakes are in adjustment and you should be ready to hit the road.
Slideout mechanisms should be checked for proper operation, but they're not likely to rust in place or bend if the slide is left open. The slideout's weight is supported by the RV's floor and the lip of the slideout pressing against a large beam in the wall above the slide opening. There isn't much weight on the slide mechanism itself.
As far as getting up to speed, I suggest something like the
Escapees RV Boot Camp. The inspection course is more for people who want to make a career out of inspecting and repairing RVs. Boot Camp is designed to bring new RVers up to speed on what you need to know when you're first starting out.
Escapees RV Club offers their Boot Camp course several times a year, the next one will be in July along with the annual
Escapade. This year it's in Essex Junction, VT just outside Burlington. If you don't have an RV, there are plenty of nearby motels and hotels.
