Re: guidance from those who've had to handle final affairs would be deeply appreciated...
My brother handled all that kind of thing, before the need arises. He did such a fine job that I didn't get involved.
However, I worked for banks for years and I make the suggestion that you ask the help of the bank manager where your father dealt.
Banks have access to all the information needed.
The hard part is that, though a person may be a bank manager, they are not necessarily intelligent, or helpful.
Find ou who he dealt with and trusted, and hire them (once you are certain who YOU trust). Together, you can form a plan.
You can possibly find an accredited bankruptcy firm where you pay a fee and your father's estate declares bankruptcy, protecting such assets as are legally applicable.
Make no promises of any kind, verbally, or written. Every creditor will try to get you to say something they can take to court to get them the upper hand over other creditors.
This is a vicious world, my friend, and there are laws against many things some people will try to do, if they think you aren't savvy.
As far as I can tell, you don't even know for sure that you are entitled to act as executor.
Find out...quickly
There is such a thing as a public trustee who manages the estates of those who die intestate. That's the sum total of all I know about the person. I wish I could tell you more.
Good luck.
Fledgling