Not sure what makes you believe so much it's a plan of Nesta or even a global national plan (the SF are a federation, the clans are extremely competitive with each other). The Sea Folk have not tried to secure land in any other nation, except Cairhien and Andor (except perhaps I forget and Harine dealt Rand for land in Tear/Illian too, but not as I recall. The SF gained not much if she did, what they want to by-pass is the very onerous harbor-fees and high taxes of the coastal nations). Nesta herself was in Ebou Dar and didn't even attempt to meet with Tylin.

Zaida wasn't there to negotiate anything with Andor, Nesta had sent two competing ambassadors, one to each city where Rand was believed to be.

It seems to me this was an idea of Harine who raised the stakes in her negotiations with Rand's Aes Sedai as Rand's demands were onerous and she knew she absolutely had to make a Bargain, so she had to make any gain she could to offset that.

I'm fairly convinced asking for land in Andor is simply Zaida's idea to counter what she learned Harine achieved in Cairhien, and what Harine did in Cairhien wasn't implementing a plan of Nesta but trying to make any extra gain she could think of to offset Rand's negotiators extremely onerous demands.

The difference is that Harine merely gained a direct access to Cairhien's market, and this bargain is worth far less than Zaida's because it was made with Rand, who may die soon, instead of with the Sun throne, while Zaida made her move far later, made a perpetual bargain binding the rulers of Andor, and at a time she understood Travelling would change everything (don't forget, Zesta outranked everyone and took control, and she let Renaille go on providing Elayne with gateways until she was in a good position to make a formal bargain over this with Elayne) and she positionned the Sea Folk to benefit massively from those new realities, and she started to trade Sea Folk One Power services to nations/individuals as a commodity, for a very lucrative price for the Sea Folk.

Note that Zaida didn't attempt to make that bargain with Elayne at first, she was rather pressuring Elayne over the Bargain she made with Nesta. It's only when she learned Nesta died and the conclave was about to start that Zaida made her personal moves.

She was very anxious to make that bargain, Elayne noticed that, because beating Harine to the finish line at the conclave depended on that (it's why Elayne ended up managing to get the private services of nine Windfinders for what might turn possibly to years (some Successions did).

That the Sea Folk now plan to use Travelling to move goods on land between nations, and on ships at sea is little more theorical than Zaida having decided to now offer Windfinders as a very expensive commodity. That last isn't theory at all, Zaida has already done it. There was nothing secret about that deal, like any good businesswoman with an eye for marketing Zaida fully expected the stories of Windfinders having Travelling and that those services were for hire by nations/individuals to spread (starting in Illian and Tear, soon all rulers would learn that) and the demand for Windfinders OP services to emerge. It was a brilliant move if Elayne succeeded, the story spreading would be that the legitimate heir of Andor managed to offset a siege and secure her throne by paying for SF services. Very attractive. Her other strategic success was to put the price asked for such services very high.

Of course there's even more to it, as it's important for its political status how much a clan makes each year... Zaida first and above all positionned her clan. Her clan now owns a land patch from which to offer goods free of the burden of "international" taxes everywhere. The other clans wishing to use that land would pay. Elayne is fairly unlikely to reconduct the Bargain with Rand for the land patch in Cairhien, not without asking Harine for more concessions (which could happen soon, Elayne could really use Winfinders help right now, especially if she's denied WO, Asha'man and Aes Sedai help).

Zaida arrived at the conclave showing the clans just how much there was to be gained from those two new trading avenues. Not only this far outshined Harine, but Zaida managed to depict what Harine has given away as extremely onerous, and binding/beneficial only as long as Rand lived or controlled the nations. Zaida, instead, made massive gains that would hold after the LB - if Elayne won her throne, of course (which ended up being the leverage Birgitte used to get the Windfinders to fight... not something that was supposed to happen... she broke the terms of the Bargain, Zaida is extremely likely to call Elayne to account for this).