> That's assuming you don't end up with a huge "out of network" bill by accident

New laws mostly take care of that. No more out-of-network doctors walking by your hospital bed while you're sleeping and sending you a $5000 bill. Also if you have an emergency while out of state your insurance takes care of it.

The "metal" plans all have the same network. The only difference is how much you pay vs. insurance.

Yeah, max out-of-pocket per year. Something like ~$24,000 family / $12,000 individual on our ACA plans. Gold and Silver ACA plans are basically identical in this state, you're just guaranteeing you pay more in premiums with Gold (so, in a bad year, the totals work out about the same, but in a good year the Gold is more expensive). We have exactly two ACA plan providers here, and their plans are nearly identical except that they have very different (both terrible) networks.

So if you get cancer you'll be paying $12,000/yr, on top of premiums (another $20,000 or so, for a family silver plan, if you're not getting assistance) until you're cured or you're dead. Two people get very sick, about $24,000 per year that they remain very sick, on top of premiums.

> For the 2021 plan year: The out-of-pocket limit for a Marketplace plan can’t be more than $8,550 for an individual and $17,100 for a family.

The Affordable Care Act stipulates various terms which result in young and/or healthy people explicitly subsidizing old and/or unhealthy people:

1) only age, location, and smoking status are able to be taken into account for pricing. And everyone must be offered insurance (i.e. no exclusions for pre existing conditions)

2) age rating factors - premium for costliest person (64 years old) must be at most 3x those of least costly person (21 to 24 years old)

3) out of pocket maximums

Figure out how low your expenses can be while still being quite happy with your qualify of life. Some expensive things don't provide the happiness you think they will.

Diversify the kinds of investment accounts you have. Maximize your tax-advantaged accounts like a 401k, but then contribute to a Roth IRA if available, and then plow money into a taxable brokerage account. When you approach retirement, plan to have some time period of expenses covered by cash on hand.

Then use cash, brokerage and Roth funds to cover expenses, while converting what you can from 401k or traditional IRA into Roth funds, and minimizing the income/taxation that results so you can still qualify for credits. Funds converted to Roth will be available for tax-free withdraw after 5 years, so continue to convert over time, while using the post-tax accounts to cover expenses.

There's a lot you can do to "engineer" your taxable income in early retirement.

Currently, if you're married, the first $24K or so is tax free. If you're in California, there are plenty of credits/deductions, so it's likely more than $24K.

Also, you can have a 401K Roth, where all withdrawals are tax free.