Have the tire date codes checked, replace tires for your safety if older than 5 years old and if they show serious side-wall cracking regardless of appearance of tires. Have entire brake system including front brake flex lines serviced and brake fluid flushed and replaced. Have entire engine cooling system checked and replace belts and hoses. Roof and dash AC should be serviced as needed.
Check operation of fresh water pump and all plumbing, water heater,furnace, awning fabric, and as mentioned above, check for roof leak water damage, need for roof repairs and re-sealing around roof vents, etc.
Your post sounds as if you may be intimidated by sales and service people. Take along a friend preferably with some mechanical and RV experience with you to evaluate what the RV service folks think that you'll need and the validity of cost estimates. If you have a mobile RV service, with a good reputation, have them inpect the rig and advise you. Expect actual repair/replacement costs to go higher than estimates. Consider cost of repairs in terms of resale value after repairs versus total costs of buying a newer/new rig, i.e. taxes, DMV fees, insurance, loan interests, etc. A lot depends on how you plan to use the rig, local camping vs touring accross the US, satisfaction with floor plan and length, storage space, etc. plus cosmetic appearance inside and out. Take your time, don't act on impulse. From my experience the roof AC unit, fridge, fresh water pump and furnace may need service or replacement when about 10 years old,