On my book, sufficient money to quit the rat race is: I own a place to live. Renting/mortgage is my biggest expense. As long as I don't own a place to live, I need to continue working.
There are lots of costs associated with owning a place beyond the mortgage. Paying off a mortgage with liquid cash is frequently not the most effective use of money since once you use money to build equity it is challenging to pull money back out if you need it.
The better way is to look at your big picture finances. You will always have costs associated with housing - make sure you account for that in your withdrawal rate.
You just get a second mortgage, how is that "challenging", people do it every day.
Paying off debt is a safe thing you can do with liquid cash until the debt is gone (with sensible emergency funds). It's a perfectly sensible thing to overpay your mortgage.
Are you a bank shill or something?
Interest payments are a loss. The less you pay in interest, the less you lose.
Anything else you do with the money is going to have a risk attached.
Getting a second mortgage is a big hassle and cost, especially if you don't have an income. You can get an asset backed mortgage but those are less common and can have higher rates.
A HELOC is certainly easier but there's no guarantee you will get approved, plus rates will likely be higher than whatever you're paying now.
My point is that getting credit is not guaranteed, and that having liquid assets has significant value. If you are not working I especially recommend prioritizing cash.
The better way is to look at your big picture finances. You will always have costs associated with housing - make sure you account for that in your withdrawal rate.