I think it is feasible to balance a full-time career with SMing, if you choose your shows wisely, maybe taking on a limited number of shows per year, and only those with a light rehearsal/performance schedules. Being realistic about how much you can, and want, to juggle, would be key. You’d have to find it meaningful, rewarding, and fun to work on small projects that can work with your other commitments rather than, say, a LORT musical. I think it would probably be easier to be corporate now and theater later than vice versa, but I’m sure either could be done.
Getting your finances together before you make SM your bread and butter is also a reasonable plan. Whether doing that is worth it to you is a question only you can answer. Same with the money; it’s all about your individual priorities. You can look at Equity salary tables online, right now, and do the math. Is that enough money for you? Are you even sure you want/will be able to join Equity? Many SMs live off of their work in theater, but I think just as many have other jobs, too. If marriage is in your near future, this whole issue is something you should probably work out together with your fiancé.
There are lots of ways to keep SM a part of your life. Whatever path you choose right now, realize it is not the path you need to stay on forever. One of the most wonderful traits among thespians is our ability to be flexible and adapt to changes.