Couple from UK buying their first RV!

Welcome, @Magor. I'm no expert on any your questions, but I'm sure folks who are will pop up in due course. I do know that it is certainly doable to buy, register, insure, and otherwise use an RV as a non-resident, because I've met folks who did so in my travels. I am also fairly certain that quite a few states will issue driver's licenses to non-residents, although not all. Because of the existence of citizens who live full-time in RVs traveling around the country, there are several services that provide a mailing address and forwarding services and thereby take care of several of your concerns. The full-timers very often have Texas, Montana, or North Dakota addresses, and usually register and insure their rigs in those states as well for a number of reasons, not the least of which being low taxes and insurance charges.