Welcome, Mike and Tracie!
Had to chuckle... most "wee" Casitas sold
are 17'ers, and they almost qualify as large by molded fiberglass standards! Compared to giant conventional Class As and 5ers, of course, it's a different story...
Casitas are very popular among retired couples. I agree that going small has some advantages. Some popular state and national parks have size restrictions. It's nice to be able to fit into two regular parking spots during grocery stops. Your tow vehicle can be a reasonably practical daily driver. Cleaning and waxing are less of a chore. Molded fiberglass doesn't have seams requiring regular maintenance. Storage during the off-season is easier.
Small will require accommodations, though. Two can't easily move around at the same time, the galley is pretty small, and the bath is a wet bath. Most lack "lounge" seating. Small and mid-size molded fiberglass trailers appeal more to folks who like to spend most of their time outside the trailer doing things and visiting places.
Casitas are popular, but there are a number of excellent alternatives worth considering. You'll learn more as you hang out here. Since you're not in a hurry, you might consider visiting one of the egg rallies near you. It's a great way to see a lot of different makes and models in one place and to meet and talk with their owners.
Used is a good way to start. You'll avoid the off-gassing of a new unit, though you'll have to avoid smoking and pet odors. And nothing beats time on the road to determine what you really need or want in a trailer. Your first choice may not be your forever choice. If you time your buying and selling right, you stand a good chance to break even or even come out ahead. Try that with a 40' motorhome or fifth wheel!