[Numbers added for reference.]
1. Yes. You have a $33K capital loss.
2. Essentially. First, the law does not give you the option to choose to defer the capital loss to a future year. You must report it on your taxes this year since the loss occurred this year.
If you have no realized capital gains this year (which it sounds like you don't), then your tax return will show a $33K capital loss, of which $3K will offset your other income and $30K will be carried over next year.
For the next decade or so, this process will repeat, eating away at that capital loss until (a) it's all used up, (b) you die, or (c) you have capital gains to offset the loss.
(I say "essentially" above because the way the law is written, you wouldn't forfeit them, you'd just be filing your taxes wrong.)
3. No. As above, you can't pick and choose when to use the capital loss. You have to report it and use as much of it as the calculations on the tax form (Schedule D) say each year.
And again, you wouldn't forfeit it, you'd just be filing your taxes wrong and subjecting yourself to IRS letters, fines, penalties, etc. Note that the broker who held your stock for you will probably report this taxable event to you and the IRS with a 1099-B in January 2022. If you don't report it or report it wrong, the IRS computers will be able to automatically see that and I think you'll get a correction letter of some kind.
4. If you're already on the ACA now and worried about your 2021 coverage, you're probably OK for this year. See "Household income below 100% of the federal poverty line." on page 8 of
https://www.irs.gov/pub/irs-prior/i8962--2020.pdf. This fall if you're signing up for 2022 coverage, to be completely honest and above board, you should take into account the $3K capital loss carry forward in your income estimate. If possible, you might be able to increase your other income to compensate - do more Roth conversions maybe, or do some more medical studies or whatever. Some people will estimate high just to get coverage, but there is risk associated with this. From the same area in the Form 8962 instructions, it says you can't claim the subsidy if "You, with intentional or reckless disregard for the facts, provided incorrect information to a Marketplace for the year of coverage."
5. Probably not. See the link and description in answer #4 above.
6. If you estimate your income too low this fall, you would be forced off ACA and be offered Medicaid. Technically you could decline Medicaid and just be uninsured.