Sales tax is one of the most common topics on cruising forums. I hear lots of opinions but few real solutions. What I have learned, though, is that if sales tax is paid in one state, other states won't ask for it. At least in our experience. A link to Florida's sales/use tax rules relative to boats is HERE
Florida, where all the snow birds go in the winter, is pretty strict about registration - if you and your boat are in the state for more than 90 days, you will have to register the boat in Florida, regardless of where it is also registered. I will acknowledge that most cruisers passing through Florida on their way to the Bahamas or Caribbean keep moving enough that no place in Florida sees them long enough to consider taxing them. Just be careful. Here's one site that explains the rules: Take Me Fishing
Lastly, the issue of mail. When we left the US to go cruising we relied on family, then friends to forward our mail to us. Family was not bad, but not great. Friends were better, but made occasional mistakes because they often didn't understand overseas mail and customs problems, and didn't have the resources that a professional mail forwarder does. We were lucky that they were extremely conscientious, unlike the family or friends of some of the cruisers we met. Because we were imposing on them we occasionally hesitated to ask for services that we have no reservations about asking of the professionals that are paid for their services.
We were referred to St. Brendan's Isle by cruising friends of ours, and have found them to be conscientious and extremely knowledgeable. We were able to order boat gear through them and trust them to ship it to us wherever we were. They also helped us establish Florida residency when we returned to the US and had no permanent residence. Our nomadic ways over the 17 or 18 years we cruised outside the U.S. didn't change just because we had returned to the US. The Internet has made cruising less complicated than before it existed, but a stateside address and professional mail forwarding service remains important to this lifestyle.
Congratulations on your giant step towards the cruising life.