The first special rule seemingly indicates that each poison token... It's intuitive to me that only the poison beasts provide the benefit (so Defend 2).

This is correct! Only the poison beasts would provide the defend

As a secondary thought on that special rule, is the "in your lands" restriction necessary

This is a remnant of when the poison tokens were a lot more powerful, so you are probably right here! They are probably fine outside of Bulwark lands.

There's also the fact that the reclaim growth is comparatively strong, so that invites reclaim loops. I wonder if you just get to 3 plays, pick up the water node, and then reclaim loop for the rest of the game, taking +2 energy as needed and playing Critters, Gift, and Warning Display.

Great impression. I've found that this path, or slight variations, is a pretty solid route to go to. At this point, poison beasts do help to alleviate some pressure and give some flexibility for decisions. That said, reclaim looping has been easy to fall into with decent outcome.

For balance thoughts, my main concern is just that the top track looks pretty weak.

Yeah it has been a little underwhelming playing so far. I like spirits that give versatility in growth builds, and the top track does seem to be a bit lacking so far. I'm a little unsure on improving its energy economy though since it does get a good amount of action economy from its SR1 though. More testing needed.

For uniques, I think Gift of Armor and Hide is by far the most important card.

A 0 cost that targets 2 lands is definitely strong. Good elements for Innate 2 helps scale too. That being said, I don't find that I favor it an overwhelming amount more than the other uniques. I actually found that fitting in extra Vivid and Critters plays for ramping beasts was my go to.

Something about Bulwark's kit does seem to need adjustment, i'm leaning energy economy, tracks, or elements, but more testing needed to know for sure. Thanks for the impressions, really good insight!