This resonated with me, as it describes my situation to almost the exact same details (including the aspirations you mention with Distributed Systems & Databases on which I totally dropped the ball with no regrets)

tl;dr: Facing the same set of walls like you, and writing journal entries about them spanning more than a year, I eventually arrived at a list of 'core values' that I go back to when life throws itself at me. This serves as a framework for me to make any important decisions, while reminding me to keep marching ahead despite the headwinds. (I pasted the exact copy of it from my journal entry at the bottom of this post)

I will re-order your questions a bit.

"How do I commit without looking back? How to think productively about dependencies between these decisions?"

- Commit but do look back. Patterns often repeat themselves, only at different scales. And most decisions provide invaluable experiences that aid us in making a similar decision down the road.

- Understand what you value in life, your set of core values or principles that serve as a framework to make all important decisions.

- Act. Move over your decision paralysis. Make peace with the fact that reasoning is infinite, unsatisfiability is core to being Human. Nature and your Mind is endlessly complex. An answer to the question we seek is often a beginning of a new mystery that is mostly turtles all the way down. So, keep re-working your core values.

"How do I limit the scope of my decisions?"

- Do they improve your understanding of your core values? Bonus points if one decision positively ticks the needle forward in multiple core values. Remember, Reasoning is the root of all values that makes us Humans.

How do I ensure I can backtrack in case of a bad decision? What is even a bad decision?

- A decision taken based on the above framework can't be considered 'bad' - as it contradicts your root value of Reasoning. All decisions will unlock an answer that you necessarily wanted - helping you set your next duck in that row. Suffering is an essential part of being Humans, and in the story of your life, bad decisions become important foundations on which success is built.

- Most mundane decisions are reversible. For the critical / irreversible ones - try to break it down into smaller achievable (and often reversible) steps - keep getting those ducks in a row. (e.g. leaving a comfortable high paying job for a more strenuous low paying one still would be a good decision, because now you've come out knowing that what you really value after all is a comfortable high paying career)

"How to find things (or thing) that I want to do and be sure to do it for longer than a week?"

- Read. A lot. Follow a ‘T’ shaped learning – broad on some topics, but deep in at least one. Explore many but exploit one. Curiosity (and hence Creativity) is a natural result of combining the functions of the Right and the Left brains, that power our Imagination and Reasoning. Think Mozart, Einstein, Doudna.

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My framework of Life:

> Be honest, especially to yourself. Respect and Recognition (our primal talents) comes for free.

> You get to re-live your whole childhood again when you raise your kids. Your memories are just playing back to you, only this time, you are in your dad’s shoes. You have been dealt a ‘Get Lucky’ card from Nature and Nurture to reach here. Use it wisely.

> Love people unconditionally. Start with your family, then the communities you are a part of. Give yourself for them.

> Get inspired by Nature, the Universe, its inhabitants, and its Creator. It has solved an amazing array of problems already.

> Build bridges between your practice and your passion, stretching the fabric of your knowledge. Wealth (our other primal talent) comes for free.

Together is how we all grow, as an infinite single stream of consciousness.

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Edits: Formatting.