Noreault's got it covered..
You'll also need all the passport info for everyone on board when you check in by phone, which you must do if coming on by water. You will have the option of checking in at various locations depending on where you will arrive.
Whether you get inspected upon arrival is hit-and-miss.. in approximately 7 importations I've been involved in over the last 5 years we've been inspected 3 times.. the rest were all done over the phone. Also you won't be paying the inpection team.. you'll have to go to a customs office within 3 days.
the only other thing I'd add is don't succumb to the tempation to lowball your price (with or without the collusion of the seller) to save a few bucks on taxes. The Border services are pretty savvy these days with market values for any model/year of boat (they can google too!!) so if you really got a great deal make sure you have the paper to back it up.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"