Considering what was written in TGS & TOM (Chapter 25), I seriously doubt the whole Sea Folk fleet is there.... or if it even fits in there.

Yes, there is a big Sea Folk fleet in Bandar Eban, but Min literally states that 'most' the ships were Sea Folk. Considering what Balwer said to Niall early in LoC about the 'unusual number' of Sea Folk vessels in 'all the Southern ports' and how we saw proof of enormous Sea Folk fleets when visiting the ports of Ebou Dar, Tear and Illian, I just can't picture all those ships in a port that's probably of a size with the ports in Ebou Dar, Tear and Illian.

So, I think there are still fleets at the southern ports and that there is also a decent sized fleet in Bandar Eban. And even if that's not the case, the Windfinders know how to Travel and the Sea Folk own strips of land in several of Rand's nations due to Zaida's Bargain.

I don't see a problem for Demandred to have the Sea Folk attack at places that will severely disrupt the Light sides plans.

My guess:
The Sea Folk will go from big suppliers of all things needed to support life in the major cities with ports, to attackers of those same cities/ ports. A double blow to the Light; from suppliers / transporters to enemies...at least for a while, untill Harine, Renaile & the Coramoor come set things straight.

I'm hoping to see burning non Sea Folk ships and ports in Tear, Illian & Bandar Eban. And the best excuse Demandred has, is to attack Ebou Dar, where the former Mistress of the Ships & her Master of the Blades were murdered by the Seanchan.

We have seen too little of the Jendai Prophecies concerning the Coramoor up untill now. My guess is, that Ishamael has been meddling with those prophecies too, as he almost certainly has been doing with the Essanik Cycle.

Once Demandred took over meddling with the Sea Folk from Ishamael (we know for sure Ishy was meddling there because there was a Sea Folk man -probably Moad- present at the Darkfriend Social as far back as TGH) he has been setting them up at positions that Sammael understood as smart moves.
I guess we'll find out in AMoL how and why the Sea Folk will attack.

I could ask you and Doma the same question, darius;
"What are the Sea Folk going to do in the next book..?"
"Why do we know 100% sure through Min that Harine will be Mistress of the Ships at one point...?"