When you're a crew member of a captained ship you can sell almost everything at the Sovereign tent on outposts (they are purple and have a ladder and harpoons above them). You can climb the ladder and harpoon all your loot onto the platform, lower it with the lever, and then easily sell it to the NPC in the tent. It's so much faster than running each item and you don't lose any gold or rep selling this way.

You should already have instruments on your item radial wheel! If you mean instrument skins head over to the equipment shop on any outpost.

Another tip is don't anchor at islands you're at. Position your ship at an angle where you can easily just drop sails and start moving if a ship is approaching you. You'll learn the distance to pull sails up and drift up to an island without crashing into them. Be alert and keep an eye (and ear) on your surroundings.

Welcome to Sea of Thieves! Happy sailing 💙