I had little success at this map but there are a few things I want to share.
1) At the coastal city in your Island, you have to train snakes (krakens may be later on)
2) You have one strong neutral in your Island and you need to see what it is before you choose your first hero. If it is a Ghost-Medusa, Assassin may make sense. You don't want to take a Valkyrie and see that the tough unit is an Archon. Barbarian is always a safe choice and he can level up at the island "IF" he takes all the cities by himself (with 85% Intelligence, he may have to take the gold site as well but I am not sure). If you have a Green Dragon at your island, I don't know what to do. Nothing would probably work there. Try the island next door.
3)First ability you need to get to your hero must be flight, unless you already have an eagle-ghost etc carrying your heroes.
4) You need to learn how to hop in and hop out from the Snake in order to increase movements of your heroes.
5) Coastal cities are not defendable. Don't try fancy units there.
6) Cities that are one move from port are very difficult to defend. They can be attacked by the land units. Don't try fancy units there either.
7) There are few ruins and the gold is limited. You will spend a lot of gold on ships etc so be wise in financing.
Good luck all.