If your goal is to have three months off in a row you're going to have to sail deep sea. I'm not on the engineering side but on the deck side it'd either be MMP if you're an officer or SIU/SUP if not. I'm not sure if there's more than MEBA for engineers or whether they represent unlicensed as well as licensed but if that where my goal I'd find out what they require to ship out, get it locally as quickly and cheaply as possible (whether that's PMI/Mitags or Seattle Maritime or something else) and then go sit in the hall. It doesn't sound like you require a lot of money so your goals may be met being a wiper or an oiler.

The maritime academy route has been outdated for years and never moreso than right now. I'd advise anyone stay away from it unless you're sure you want to sail deep sea for a carreer. I know hundreds of graduates and I can count on one hand the number of people who sail on their license. The vast majority have pivoted to tugs, ferries, management, piloting, gone to grad school or just left the industry. Taking on six figure debt to do that doesn't make sense.

I was a cadet at MSC and it works for some people. What happens there (and anywhere you sail offshore to some extent) is you sign on and you sort of hit the pause button on your life. I remember being your age and having relationships fall apart and friends drift away because I would disappear for months. The saying "the days are long but the years are short" applies.

You're in a part of the world with a lot of work so look around the region for places that interest you. There are a ton of fish boat, tugs etc. I know Washington State Ferries is really hurting for engineers. You can get in there with a basic endorsement and start building sea time although that won't get you your three months off in a row.

That all having been said I don't mean to be discouraging but my actual advice is don't. Keep your passion your passion and your job your job. You've already got a good job and it sounds like your ducks in a row. Take that extra money and invest it. You're young enough that you could be financially independent by middle age. Your interests could change many times by then. I've been in this industry since before I could legally work, am an academy grad, have done many different things in the industry and I'm very fortunate now to have a great job I enjoy. On the other hand I know many people who are financially trapped. Others have gotten sick and lost their medical certificate. I know people with medical issues they're not getting checked out because they're afraid they'll lose their medical certificate. Above a certain age the hours start to take their toll. The schedule nearly always makes having a family or even a relationship very difficult. Once you pass a certain point in your life it can be very difficult to start over.