This was the first time I was working with a ship with sails and they are a very different experience. It took some getting used to, but I found a couple things to help with the process as you're working on this set.
First off, you're going to want to paint the raised symbols on the sails before filling the rest. There are a lot of subtle shade and tint transitions to remain faithful to the box art. Even if doing your own thing, the raised areas are shallow, it's almost a given you're going to bleed off the raised surface onto the sail. Better to bite the bullet and make sure the symbols are correct before you proceed; they're going to command the lion's share of a viewers attention.
I highly recommend you find a foundation color for the sail itself. Filling in the areas around the symbols will be less painful with the superior coating of foundation or black.
Mask your contact areas and pre-fit every piece before gluing. This is a kit that has zero room for error; even a coat of primer will make it impossible for the joins to fit properly. I use a piece of kneaded-eraser to keep the contact areas clean during priming. It's cheap, reusable, and effective.
And don't forget to keep painting those tokens.
Two ships in the Grand Alliance complete. Next up is the Swordfysh.