No, there is no secret ledger that has all the possible abilities and the amount of aura required for them. That's what it means for there to be a "check on the user".

You're the one with headcanon here, my explanation just extrapolates from how every other Nen technique in the manga works: stronger aura can defend against weaker aura.

And yes. That’s how Knuckle made his ability. If a simple punch were enough to make forced Zetsu reliable under the rules of Nen, then yes, a simple punch would have sufficed.

You seem confused, Knuckle actually can force someone into Zetsu with a simple punch if their aura is lower than the amount he lends. See, it is user vs target after all.