So I have an idea for a game I'd like to publish on storefronts. I've already looked into the steps to do that But when it comes to unreal development I'm a novice. I don't need help with building the game but more how to structure development.

1. What are some best practices for workflow. Should I work for a specific amount of time test what i've built. if its works how I intended should I clone the project at that point and save it as version X? and continue to do this as I add more complexity and systems into the game. keeping documentation as to what I added so I know if something is broken I can look back and figure out where I went wrong?
2. I plan on making a 3rd person puzzle game with the environment being a large portion of the game. should I start by greyboxing and designing levels? or should I focus on other stuff like mechanics that will interact with the puzzles.
3. When should I start worrying about audio and sound effects, also any rec's on good asset packs or tutorials for this would be appreciated.
4. marketing is another concern. I planned on handing out copies to friends/family, online communities I'm apart of and even a fairly large streamer I know personally who also runs a large gaming website to get exposure. are there any other avenues I could go such as facebook ad or reddit ads that won't kill my bank account.
5. general file structure advice also wouldn't hurt as well. I assume it would be best to keep all my interactive props and static stuff in different folders. same with any terrain pieces I plan on reusing. any other advice would be appreciated.