Because its a fiberglass roof, its much easier to fix than a rubber roof. You can scrap off the old caulking with a putty knife without worrying about damaging it like a rubber roof. You can also completely clean off remaining caulking with varsol which you cannot use on a rubber roof. Replace all vents assemblies, even washroom vent assembly with motor, not too expensive. Use Dicor roof calking to re-seal vent assemblies and joints between front and rear caps, shower skylight,etc. maybe even replace the Fantastic fan as it uses a plastic frame which may be cracked and can leak.
As mentioned, the roof is the most important fix that should be done before using and risking water leaks.
Use an oxidation remover like Meguiars Mirror Glaze #49 Oxidation Remover Heavy Duty Cleaner to clean up and bring a shine back to any outside areas that look bad like lower doors, rear cap, lower fascia, etc. Don't sand.
The hydraulic levelers have springs that retract them. Try spraying silicon lub
on the hydraulic levelers when extended, this may allow them the retract correctly.
Not sure of the no AC problem on rear slide, Check AC breaker panel for tripped breaker to start with.
