Our ACA plan for a family of 3 is about $750 per month with subsidies. (Many people pay much less) We don't have any medical issues that significantly impact our lives, but we do spend regularly. So, we chose a plan with a $3,200 family deductible. ($1,600 individual) There are $0 deductible plans available, of course at a higher monthly premium.
I was worried when we moved to Texas in 2020 that, since the State did not support the ACA, choices would be sparse. There is no perfect plan, and there are some bad plans. (Not just bad for us, but seem like bad deals nobody should take) But it has definitely been doable, with some forethought. While you have serious medical needs, you do have one good thing: you know what they are. As I said, you can select your immunotherapy and use it as a search criteria for the ACA plans available to you.
You likely won't get everything you want in a plan, but you can prioritize the things you want most.
In terms of withdrawal, I agree with
@joe189man . I am 52, and withdrawing from my taxable account only--and greatly enjoying the 0% long-term capital gains tax rate! I do taxes early, in November each year, and balance my ACA subsidy with the gains from my withdrawals during the year. I usually end up with a nonrefundable credit, due to the child tax credit. I absorb this with a Roth conversion, and may do more in the 12% income tax bracket depending on our cash situation. I don't yet have a clear projection of where we will be regarding RMD's, but we seem to be trucking more or less to plan, with the taxable account sustaining us until 59 1/2, and still having flexibility after that with taxable, trad IRA, and Roths to potentially draw from.
One more tool in the toolbox: my employer switched us to an HDHP many years ago. We were pretty good with our FSA, and the first couple of years treated our HSA much the same. As our circumstances improved and I thought more about early retirement, I stopped that and invested it. Our HSA sits at about $70k. I view this also as a type of health insurance, in that if we were hit with a big event and a big bill, I will pay for it out of the HSA, instead of withdrawing more out of taxable, and throwing off our tax/subsidy balance. If the HSA survives until 65 and Medicare, then we will draw it down then.
I don't know of any book on withdrawal strategy to this level of detail. There are numerous blogs that do, but they will have a slant of "this is what I did," rather than "research shows this is what most people should do." One place to start is
https://earlyretirementnow.com/ ERN goes into excruciating detail, so it might be overwhelming. But some of us find such thoroughness fascinating.