Retired with assets: is D7 the way to go?

If there is an existing discussion or trustworthy web site that answers my question, please direct me to it.

I'm 59, US citizen, with at least 1.5 million in my retirement savings. Most of that is after tax, so I won't pay taxes in the US when I withdraw it. I am on Social Security disability, and I receive $3000 per month from that.

I have a NIF through a Portuguese lawyer.

I have a friend in Lisbon who would be happy to host me until I find my own accommodations.

I am not as mentally sharp as I used to be (this is part of my disability), and I am confused about when and in which county I need to apply for the D7 visa.

As I understand it, I can visit for 90 days without a visa. I have a Schwab account, and setting up a bank account with $10000 euros should not be an obstacle once I am in Lisbon. Am I wrong about that?

Once I am in Lisbon, what is the easiest way to apply for the D7? Would I need to fly back to the USA for the visa application? Would I need to stay in Portugal, or in the USA, while the visa is processed?

I am reasonably certain that I qualify on financial grounds, and my criminal record is clear, but the when and where of each step confuses me. I am willing to pay for expert help if I must, as with the NIF, but I don't want to waste thousands of euros on tasks I could accomplish myself.

Any advice on how to proceed would be appreciated.