::)1: is it better to go to Fl. and get our domicile address first before buying the rv?
If you no longer have any ties to your current state (i.e., you are not working or do not own a house in which you live), then the answer to your question would be yes...get your mail forwarding address set up first and register your vehicle in your new state of domicile. Check with your new state of domicile to see how much time is allowed to lapse between registering a vehicle and when you have to get your driver's license (in South Dakota, for example, that period of time is 90 days...I don't know what it is in Florida).
2: do you have to take a written test when changing your license to that state?
I'm not familiar with Florida driver's licensing rules...hopefully, someone here is domiciled in Florida and can answer that question for you. Alternatively, you could call Florida DMV and ask.
3: Can ya get a loan like this without haveing a house as an address?
We first started fulltiming back in 1998. During that time we've purchased RVs and automobiles, all using our mail forwarding address, without a problem. We never advertised the fact that the address was a mail forwarding address (always used "#" instead of "PMB") and we never advertised that we were fulltime RVers. Had we been asked, we would have told the truth, but the questions never came up.