If Na'asiyah is my only Tactics hero, can she "pay" for Dunedain Hunter? He costs 0, so she's not using any of her resources to pay for him, which is her limitation: " Resources in Na'asiyah's resource pool cannot be used to pay for allies."

Seems fine, unless somehow "0 resources" breaks the rule, but that doesn't really make sense as she's still not using any actual resources to pay for him.

Yeah, that works since you're not actually paying resources from her pool, which is the stipulation.

Similarly, pairing her with Grima for cheeky Vassal of the Windlord or Knights of the Swan plays should work.

(almost similar thought/question here, that is why I do not open another topic)

when having no spirit hero (and no songs, etc.), would it be possible to put Curious Brandybuck into play via his Response? It sprung to my mind that the answer should be a Yes, right?

Rules:: Cards with a cost of zero do not require a resource to be spent in order to pay their cost, but they do require at least one hero under that player’s control to have a resource icon that matches the card’s sphere.

Says nothing about heroes being allowed to spend resources of the relevant sphere. So, yes Na'asiyah enables playing zero cost tactics characters (this is the natural inverse of the well known result that Elrond can't enable them).

This rule says nothing about costs in trigger effects, only costs/restrictions to play a card. The Curious Brandybuck effect is a " put into play from your hand" not a "play this card"-style effect so it's certain you can use it with without a Blue hero if you are so inclined.

thanks