If you have family HDHP coverage and no other medical coverage, you can contribute up to $8300 per year, plus $1000 catch-up since you are over age 55. That breaks down to $775 per month for each month that you are covered by a qualifying HDHP (and have no other coverage) on the first day of the month. You don't say if your spouse's coverage option is also an HDHP or not. If yes, you could contribute $9300 for the year ($6800 additional). If it is not an HDHP and you switch to your spouse' insurance effective August 1, then your HSA contribution limit for 2024 would be 7 months x $775 = $5425 (from the $2500 already contributed, that would be up to an additional $2925).
The advantage is that you can contribute money, take a tax deduction, then withdraw it for qualified expenses that you would have to pay anyway, and be able to get a tax advantage on those costs. You are not limited to payroll deductions, you can contribute your own money out of pocket.
You can fund your HSA from your IRA, however you can only do this one time in your life and your overall contribution limit is still the same, so your maximum qualified funding distribution would be either $6800 or $2925. However, there is no tax deduction for doing this, since the IRA money is already pre-tax. You can't directly fund an HSA from a 401k. The only reason to fund your HSA from an IRA is if you have significant medical bills and can't pay them unless you withdraw from the IRA. The QFD allows you to move IRA money into the HSA so you can then withdraw it and pay your bills with tax-free money instead of withdrawing from the IRA and paying tax. But if you can afford to deposit money in the HSA and then withdraw to pay the bills, you get the tax savings.
The lowest HSA maintenance fee I have seen is $3. You will have to shop around and see what you can find at different banks.
