Extended warranties - we don't believe in them. Instead, sock away some $ each month just for repair purposes. Hopefully, you won't have to use it.
Clubs - If your trips are casual, not structured, you might try out Passport America for 1/2 off camping. They do have restrictions and the campgrounds aren't on the interstates for the most part but it would be worth the cheap membership fee to give it a try to see if it works for you. A few nights of camping fees pays it off. Others such as Thousand Trails, etc. are very expensive to buy in and depending where your travels will be, the parks are not everywhere.
Magazines - since you're new you might give Trailer Life a try. You will get some useful hints from it along with a travel article or two and advertising to learn what you now need to buy!
Places for information - right on this forum. Explore the various forum sites to find the ones that fit you best. When you're planning a trip - go to the RV park forum and ask away. Most folks will give their help - even if it's once again asking for route or campground information to Yellowstone!! :)
Lastly, don't be afraid to 'wing it' by traveling and not making detailed plans or reservations if your time is free. Just plan a general direction with possible stops. It's a more enjoyable way to go. Also, don't stick to interstates. Get off on the secondary roads and you'll see much more of this beautiful country.
Welcome to the RV world. You'll surely enjoy it.