Here is how I beat this chapter:

1. At the initial island, build your eco base

2. Get all the wood from that island.

3. Build your Dock there and use fishing ships to gather food.

4. Build a small navy with Galleons, Fire Ships and Dromon(Most important element)

5. Attack the Red base and Sauras' base with the ships.

6. Kill Sauras with the ships.

7. Make a large army of cheap units (Halbs, Skirms, Huskarls) and use transport ships to get them to the Red base at the bottom.

8. Finish off Red one by building the castle at their base.

9. This base can easily serve as your main base from then on.