With an old rig that has been messed with by one or more previous owners, it might save you time and aggravation to find an RV service that has an expert on RV electrical systems. There may also be an automotive electrical service that has somebody with good RV electrical experience. Make sure that the converter/charger and house batteries are working properly to power your interior lights, fresh water pump, electronic appliance controls ,etc. also make sure that your 120volt system is working properly to power the roof air conditioner , and microwave. Tires must not have deep sidewall cracks and should be no more than 5 years old by DOT date codes embossed on tires.
Brake system including front flex brake lines should be serviced as needed and old brake fluid flushed and replaced. Engine cooling system including water pump , radiator and all belts and hoses should be serviced as needed. Breakdowns on the road are expensive and some ( tire and brake failures) can be dangerous. Be prepared to spend some serious money to make your rig reliable and having "most of the comforts of home" Good luck with your new hobby.
