A few general suggestions:
1. Consider renting a motorhome for a few days or a week before purchasing one. You'll learn a fair bit about what it's like to use and drive one, and be better able to evaluate what features, floorplans, etc. would work for you, and be a leg up on understanding the systems of an RV.
2. I would generally not recommend buying new for your first RV. I'm not sure I'd buy new for any RV, personally, since the initial depreciation is pretty high and more often than there should be there are a bunch of--hopefully minor--initial defects to work through with the dealer/manufacturer. Let someone else take the financial hit and annoyance.
3. When it comes time to look at specific models to maybe buy, I suggest taking time to do a "dry run" of as many daily activities as you can--preferably physically, but at least in your mind. Go through the motions of dressing or undressing, cooking a meal, watching TV, reading a book, using the bathroom and shower, etc., and give thought to where things might be stored and whether you'll be forever bumping into a cabinet and so forth. Is there a good place for a trash can? a laundry bag or basket? Can you access the bathroom or fridge after pulling off the road without needing to deploy a slide? Is there room for your cutlery, your dishes, your coffee percolator, and your saucepans?