You'd really better ante up a couple of hundred bucks for an attorney or a broker who is familiar with the laws.
You are consistently snipping at bits and pieces of a bigger picture and since you're not aware of the whole
picture regarding tax liabilities, the odds are you are going to get into big trouble, or at least a big tax bill, if you don't get pennywise and pay someone for proper counsel.
The $18,000 limit in Florida
is not a TAX limit, it is a SALES tax limit. How that sales tax is imposed depends on where you are a resident, where the sale
takes place, and other factors. And if you are bringing the boat into the US from outside the US, there may be import duties as well.
Folks who can afford to play with expensive toys usually do pay the pittance that a good attorney (broker, agent, etc.) will charge them, because unless you understand the WHOLE PICTURE, you're going to wind
up paying more when you don't pay for professional advice. They'll know all the questions to ask you, to make sure you don't miss something.