Check all appliances/systems (fridge, stove, heater, water heater, water pump, faucets, lights, battery power, generator, propane, shore power, air conditioner, etc.) - if they won't let you hook up the water, or plug into shore power, etc., then walk away.
Check all rubber (hoses, belts, fuel lines, etc.). Check for fuel leaks (engine and generator) and propane leaks. Get a mechanic to check out the engine.
Plan on putting at least a couple thousand within the first year to get the RV "road ready". You might be able to do some close to home trips while getting things up to par, but not long distance. Depending on the RV, the price you paid, the quality of your inspection, the honesty of the seller, etc., you may put anywhere from $2000 to $10000 into the RV AFTER purchase.
Don't worry that much about low mileage - in RVs, it's not always a sign of a good deal. An RV with lots of miles has been driven extensively - meaning things were working for most of the RV's life. Many people get rid of lemons quickly because they could never get them out of the driveway.
If you're going to finance, check with your bank/credit union. Many will not let you use an RV or auto loan for an RV over 10 years. Most small RV dealers don't offer in-house financing - they work with your bank. You may have to do an equity loan, personal loan, etc. or pay cash.
Really think about what you want, how you want to use it, etc. Think about living in that floorplan. Find out if there are size restrictions to the places you want to visit. Are you going to spend all your time at the campground? Or do you plan on going into town, sightseeing, getting supplies, etc.? Do you have small kids? Consider child seats, booster seats, etc. Will you have full hookups? electric only? None? Do you need to tow a small car? boat? etc.?
You're getting an early start on things and that's good. Make lists - must haves, would like to haves, don't wants, etc. When you think you've researched enough, go back and do some more.
