Def bet on yourself.
One thought: time and ownership. If you are building the US for them, that is a huge market, regardless of industry. You said it will increase their company by 50%. That is crazy. That will require work like you may have not done before, assuming they are already large, based on them being a global company and having officers in different countries. This might require the kind of work where you sleep a lot less, get a lot less weekend, and make fewer soccer games. If you are down, cool. If you aren't, cool. You should definitely find a way to get a measure of what that might look like/require and you should definitely weight that against $40k or and/or any % of ownership you can squeeze out of them.
Balance is really rough ridin' hard. You are about to enter a family period of time where it might be the hardest. My advice would be to keep balance in mind during this process unless you are the kind of workaholic that likes work being #1. If you are, cool, no judgement, one of my besties is that guy. Just don't go into something like that without evaluating workload and balance against a gig you like and already have.
This is a mental health PSA, here.
