If you want to develop marketing skills here's some things to research: Start with something called "product marketing" the job titles are typically "product marketing manager" and these folks are typically a group that sits in "marketing" and does things like "messaging & positioning" figures out "pricing & packaging" and comes up with all the info about the product. Basically, works with Eng + PM teams and packages up all their work and makes something you can actually sell. Just spelling this out since you can google it on your own. Look for something called "totally addressable market" (also know as TAM) too and that'll give you the size of the market you're selling into. Some of this is sort of art and science since there is nothing really exact and you will need to test it via trail and error. But, it'll get you pointed in the general direction of what's correct.

FWIW, I agree with OP here. Kids are a game changer and having a stable paycheck coming in gives you time to dedicate to your family without stress. This is highly underrated in the first 3-6 months when you're trying to figure out what this new life looks like (living on 2 hour chunks of sleep). Speaking from experience trying to start a company, having a kid, then quickly realising I need a job asap.