How long are you going for? Don't obsess over possible things that might go wrong. Just go and enjoy it! Don't try to do everything in one trip. Relax! its vacation! Definitely stay on site. We stayed off site the first few years we came. After the last trip off site (and it was in a nice hotel, not expensive, but nice) I didnt want to come back anymore. Then we decided well, lets go one more time and stay on site and we havent looked back yet. Our first on site hotel was POR (Dixie Landings back then) and it was great and well worth the price. Then we discovered the DIS and all the discounts available. Don't over plan. That can make you really frustrated if your plan doesnt work like you wanted it too.
Good luck and have a great time!