Have brake system checked for sticky calipers, flush and change brake fluid. Have tires checked for serious sidewall cracking, replace tires if needed. Tires may thump until you drive some distance at moderate speeds, if thumping continues, tires may have tread separation. Check cooling system belts and hoses.You probably have to replace propane gas alarm. House battery(s) probably need replacing. Test run generator with roof AC plus microwave on. Test run furnace and fridge. Change fuel filter after some driving.
Other recommendations are good.
Our rig hasn't been driven much in last 3 years, but I ran engine, generator, roof A/C and furnace and drove it to have it smog tested recently. Getting back into RV'ing after two knee replacement and other surgeries, our rig needs TLC also