Hi there, good work ! Profesional project manager and coder here (for over 15 years), although not as a game coder. I work with black magic and voodoo, i.e. mostly C/C++ and assembly.
I do some game coding on my own and plan to make one that may appear here, but I lack asset making skills. Also, still not decided wether i want to do it as an html game or something with less text and more interaction from the user. I guess it needs to be playable one handed...
The guide is very good. I'd add some recommendations about management and coding. Coding is frustrating because really, 99.9% of errors are due tothe coder doing something wrong. And the remaining 0.1% too, but no one wants to admit it. In my line of work, that 0.1% is sometimes due to a hardware error, but modern OS completely abstract that.
Add unit tests. This is probably the most frustrating thing to do, but it will save the coder's ass and time many, many times. If you are writing a function that supposedly does something, write unit tests that make sure to test this function's output depending on its inputs. It is very important, as with time the function may evolve, and the only way to make sure it works as intended is to replay the unit test, automatically of course.
Second one, as you pointed out, organisation is important. Break down the project as tasks, with dependencies. Use software to track that, there are tons. Choose one with a ticketing system, and associate it to a version control system.
Every time you work on a task, "commit" the work using the version control system, with a ticket number that associates it to a task. Have it run a build and unit tests automatically on commits. Gitlab is very good for that. Version control can be used with assets too, although it usually is not. This is important as sometimes you need to go "back in time" ... and it is necessary when not working alone. If you do work with other coders, make it mandatory to review code before commits.
That last pararaph mostly applies to games that need coding though. I am not sure it can apply to html games.
Finally, make backups. I dont think there is anything more frustrating than losing months if not years of work because someone stole your laptop, the hard drive dies, the house catches on fire or you just get hacked. Make backups on a regular basis, and store them in a different geographical place. This can be easily automated through rsync for example.