◇ Could this help me?
Yes for having the file, with a size correction. The central point is correct and is the highest-leverage single change most people can make: an agent that is told the layout, the conventions, and the purpose of a project stops guessing, and the same context stops being retyped every session. The part to treat carefully is the implied contents, since who you are and what the business is can expand into pages that are paid for on every conversation and apply to almost no individual task, and the research on instruction counts says that makes everything else in the file less reliable. General practice, and the honest version is to create the file immediately and then keep it as short as it can be while still answering the questions that come up repeatedly.
Help me write a project instructions file from scratch, optimized for being read on every single conversation. Interview me about this project rather than guessing: how the folders and files are organized, the conventions I expect followed, what the project is for, and the mistakes you would otherwise make here. Then write the file including only what applies to nearly every task, and keep a separate list of the things I told you that are genuinely conditional, with a recommendation for where each one should live so it loads only when relevant. Tell me the instruction count of the finished file and which instructions you would cut first if it needed to be shorter.