Detective, there has been a lot of good advice here. There is a lot you need to learn, and only you can tell how much time you have to learn it. My suggestion is to start with two things: a mission profile and a study of manufacturers. You will need to figure out how you will use your RV. Are you going to go somewhere and stay for a month or two? If so, a motor home probably isn't your best bet. Are you going to be on the move frequently? A motor home sounds good.
While you are working out how you will use your coach, you can start investigating manufacturers. Foretravel, Newel, Newmar, Tiffin, and Winnebago usually show up on high quality motor home lists. I would add the Bluebird Wanderlodge to that list. Get on each of their forums and just read for a couple of weeks, and then start asking questions. Go visit the factories - all of them if you can. Bluebird is no longer in the MH business, and that turns off some people. However, their owners forum is outstanding, and there is at least as much support there as from any factory.
While you are in Nacogdoches, Texas, to visit the Foretravel factory, take a day or two and go over to Houston to PPL. They have hundreds of RVs for sale, most on a consignment basis. You can spend as much time as you like looking at all sorts of floor plans. It won't take you long to figure out what will and won't work for you.
It won't take too many months before the hundreds of coaches available is narrowed down to a much smaller number of coaches that will work for you. THEN you can start carrying your checkbook.
As for used versus new, my suggestion is to buy used at first. Later on, when you are much more experienced, you may decide to buy a new coach that is built to your desires. That's the time to do so - not when you don't really know what you want. Many people go through 3-5 coaches before getting the right one. Some people have been known to trade coaches twice in the same year. THAT can get expensive!
Good luck, and enjoy the learning and hunting.