Who starts probate?

The executor(s).  If he didn't leave a will so one hasn't been appointed, the next of kin who is most likely to be appointed administrator by the probate court, which according to the law where I live - assuming he had no spouse or children - would be you.

So it's your job!  If you don't know what to do, see a lawyer.  Any lawyer will do as probate is one of their most frequent jobs.  After all, everyone dies.  My deepest condolences on your loss.

You might not even need probate if the boat really is his only asset, you will if he has money in the bank, but again a lawyer can work that out for you.

You, his wife, an adult child.  Really anyone.

If no will appointing an executor then family can initiate.

A Florida estate can qualify for summary administration under one of two circumstances. The value of the decedent's Florida probate property doesn't exceed $75,000 as of 2019. This limit does not include the value of the decedent's protected homestead real estate.  Best talk to a Florida probate lawyer.

If he left a will, the executor.  If there was no will, the next of kin.

You do. Talk to an attorney