Welcome to RV.net and the upcoming world of RVing!
Make plans to go to RV shows. Look through the rigs, take your time! Take a pen and pad with you. Look for things that you like and more important things you don't like.
Think about what type of camping you plan to do. Are you taking pets? Children?
Don't let a pushy sales person get you into a rig that is too big, expensive or has expensive items you will never use.
Once you decide on a rig, then think about items you need. Setting up camp will become very easy. Many items will come from some dealers as a starter pack. If you buy a used rig it may come with some items.
Many items are basics. Good drinking water hose, sewer hose(we like the Rhino Flex), outside chairs like the folding bag type. Once you go on a few short trips you will see what you need. No rush to go out and buy everything at once.
Interior items are more important. We have our rig set up to go immediately. Dishes, pots, pans, tableware, glasses and even some food is always in the rig.
Good luck on your venture into the New World!