42, hoping to semi-retire by 55. A couple questions

I started saving about 6 years ago. currently have about 160k in a traditional 401k, 40k in a roth IRA. I love my job, but I don't love having to work 36-40 hours/week. I have a condo that will be paid off in 13 years, when I'm 55, and I'm thinking that's when I can partially retire, or maybe even earlier if I can throw more at the condo principal.

Once the condo is paid off, my monthly expenses in today's dollars will be roughly $2000-2500. If I work one shift a week(12 hours), that would cover my expenses with the condo paid off.

I think like most people considering FIRE, healthcare is a major concern. My fiancé is 6 years younger than me and as of now, has no desire to retire early. *Will I be able to file separately to keep my income low enough for the ACA subsidies?*

How would you guys allocate future investments? I'll max my roth IRA regardless and contribute at least a few thousand/yr into a HSA. *Should I be contributing to a 401k and taxable brokerage, or is just the 401k good enough?* If I wait until 55 I can take advantage of the SEPP 72(t). I suppose if I want to semi-retire before 55 I would need a taxable brokerage. I don't anticipate needing to pull a ton using the SEPP, just 10-20k/yr max. Or I might still be willing to work some extra shifts here or there and could leave my retirement accounts alone, who knows.

I'm also thinking about shifting some of my 401k investing into paying off my condo sooner. At a 6.5% rate, I know it doesn't match market returns, but it's also guaranteed so idk.