How do I decide between building and buying?

Guessing feels bad here because the stakes are real and you sense you are missing a way to think it through. The good news is that build-versus-buy is not a matter of instinct. It follows a few plain questions, and once you have them, the fog usually clears. You do not need a guru's framework — you need to ask the right handful of things honestly. Start with these. Is this thing core to what makes you special, or is it plumbing everyone needs? Core things are usually worth building; plumbing is usually worth buying. Does a good option already exist, and how close is it to your needs? What will each path cost you not just now but over years, in money and in attention? And how badly does each lock you in? Those questions do most of the work. So for the decision in front of you, write those questions down and answer each one plainly for your case. The answers will usually point clearly in one direction, and where they don't, you will at least see exactly what you are trading. That is not guessing anymore. That is choosing with your eyes open, which is all anyone can really do.