simple question, just wanting to know the majority of how people do it.
That's what a day job is for.....
I've been lucky that my day gig allows me to indulge in gear purchases every year and still leaves me plenty to live on and take care of everyday expenses, plus put enough aside for retirement.
I have no kids...so that certainly adds plenty to my "gear fund"!
I've sorta done some of my gear buying in chunks. Initially I dropped about $30k on my console, tape decks, some outboard gear, mics, etc...etc...etc.
Then one year I spent like $10k just on assorted mics. For a couple of years after that I bought a bunch of guitars.
I was on an amp buying binge the last couple of years, and got rid of all my middlin’ amps and went up to the "boutique" level for my entire line.
Right now I'm fairly well set in my studio AFA gear, so now I can just "fill in" on whatever is missing with accessories and nice-to-haves...though I've been buying lots of stomp boxes the last year.

I'm also thinking of some new outboard preamps and comps, though I already have enough...I just wanted to go up another level and also try some new flavors. I'm also going to be upgrading my DAW in the coming months.
I sell off my old/unwanted stuff on eBay and then use that money to buy new stuff, but I'll supplement with additional $$$ as needed.
The way I see it...my studio is very well appointed at this time for a personal project studio and I could easily open my doors and do more active commercial recording, though I honestly don't need to, as my gear is paid off and my day gig pays much better than I could make with a small commercial studio gig...though yeah, I could still do it on my 3-day weekends, since I only work 4 days, plus I have a lot of personal, liberal leave time, so it would be easy to cover longer, more involved projects...but again, I really don't need to get into all of that at this time.
Maybe if/when I retire, as I'm hoping for an earlier retirement...but at this time I'm enjoying my studio for my own use and the occasional outside project, and maybe that's what I will expand on...a few hand-picked, occasional, outside projects, as I don't need to book a lot of studio time in order to pay for anything.
I'm also looking for possible band situations to get back into…so I’m sure that will also spill over into the studio at some point.