Thanks, Daegan. The moon base is gonna be hella dangerous, so I'm planning to make them pull just about every time they do anything, unless they can come up with a really good specific character reason to automatically succeed.
I'm also planning on using a house rule to reward the players that show the most initiative and make the most pulls:
I have a second set of Jenga blocks. Each time a player makes a pull, they also get a block from the second set to keep in front of them (that also lets me easily see who's been making pulls, and who I might need to prompt with some character danger, to evenly distribute spotlight time). Once a character has at least three blocks, the next time they make a pull they can instead opt to place all of their kept blocks on top of the tower, forming a whole new layer (though they must explain how one of the facts from their character questionnaire helps them succeed). That rewards them for making pulls with a brief respite of almost-guaranteed success. Plus the tower will increase in height as the game progresses, building more psychological tension.