"Well, here I am on Island 1. What am I supposed to do?"
Read what the character writes into his diary. It's helpful stuff. Apart from that: just advance through the "tech tree".

First make 7 buildings and rock yourself
(rocking is just a joke)
Then after making 7 stuff you will get a lockpick
open the crate behind the hill
Get the spade and map and then rock yourself again
thats the most helpful hint without any spoiler

well after you dig for the treasure, the pirate comes out you will need to catch a parrot with a net (fairly hard). then if i am not mistaken you have to fight claw monkeys while digging for more more treasure.

Is there an obvious middle tile? it should be the square in the middle on the floor.

yeah you cant go back. If I'm not mistaken you are at the island were you are surrounded by Rapters right?

Get the Golden bow and arrows at all costs! Slowly kill off all the rapters and their nests while building a base at the top of the mountains. I totally forgot how to get off this island. sorry. let me know what you see and i will get back to you.