Ladron
Many good technical advice has already been given here on what measures can be taken to achieve maximum security and maximum anonymity.
I would suggest to step back and ask yourself:
Can your life or other important assets only be protected by such extreme measures?
If the answer is yes then you definitively have to take a step back, consider your often cited threat model, and build up your measures from the ground up accordingly. Failure is not an option, your enemies have nation-state resources so be strict and thoughtful and don't just randomly take measures.
The answer is no - security and (a certain degree of) anonymity are important to you, but your world won't collapse if you fail (that's what I assume because not a lot of people have such a high threat model)?
Then i would advice to take it slowly—especially (unfortunately, I can't tell from your post) if you haven't cared that much about security and anonymity until now. Your journey is not a sprint but a marathon: The topics of anonymity and security are too fast-paced for you to develop a fire-and-forget-setup once and never have to worry about it again and going from 0 to 100
New here with limited tech skills
can mean a steep learning curve.
Extreme measures entail a high level of responsibility - losing access to all your important data, privacy fatigue, and social implications are just three real and serious threats that immediately come to mind which shouldn't be underestimated and therefore be taken into account.
Don't forget: You're already doing great, using (one of) the most secure mobile operating systems in the world and being curious about privacy and security. That alone puts you ahead of the game.