You can access the tutorial at any time on the main menu.
Is the tutorial just that wee starter island, get a ship and then leave through the fog? Can I go back and replay the tutorial with my main character with the gold I've accumulated and get that hidden gold on the island or do I need to start a new character?
Everyone who starts a game gets their own ship. To both be on the ship, one person starts the game and invites the other to the crew.
Yes. But you need to sell everything before you logout, it isn't saved across sessions.
So anything you leave on your ship is gone the next logon including any supplies like planks, food etc that I've stored in barrels, all of it reset each time? So only really stock up what you need for a sess and then sell the lot before logging out? Pity, would've been nice to stock up your ship, park it at a safe spot and log out only to come back in to where you left it with all the stuff on it, did the Devs give a reason for not doing this? How do you form an attachment to your ship if it resets each sess? Or am I reading you wrong?
No you spawn at a random Outpost every time you login.
I Take it the main gameplay loop is head out, plunder explore and then make a beeline for the nearest outpost to sell everything
Skulls - Order of Souls
Chests/trinkets - Gold Hoarders
Cargo - Merchant Alliance
Mermaid gems can be sold to anyone. Whoever you want the rep from.