Questions about general process of making a game

Hello everyone.

TL;DR: if you were to explain to someone over drinks what kid of process you would follow to make a basic game, what would that be? In what order do you focus on game story, level design, character design, audio…processing(? Is that the right term?), etc. What is important and worth the investment of time to really focus on and what has been found to not always need so much attention?

The quick version of my situation:

I know how to program, though it has been years since using C++. I’d like to get back into using it and game development really is the only thing that uses it that I feel like it would be worth my personal time to invest in. As I mentioned this to my wife, my kids overheard me and one had an idea for a video game she’d like me to make. I thought it would be a great thing to do for her, as it gives me a goal and someone else who will be disappointed if I don’t finish it. Now, I have a general idea of what I want to have as a game but I’ve been around the programming block enough times to know that I know only about 10% of what I will end up needing to know to make anything that is passable for my kid to play. I’m not interested in putting this out there for others to play, I just want this to be for my kid. So this doesn’t have to be amazing on graphics or audio quality. In fact, I intend to make it low-poly so it can run on lower-end machines (i.e. the kid’s computer).

I know there is plenty of content out there, both free and paid, to cover just about any specific topic I want to know more on. So I am less concerned about where to find tutorials, though I will never snub a recommendation about how to learn a skill, and more concerned about the overall process.

Now on to the long-form of the post.

Basic overview of the game:

I have an idea of what I want for a very basic game, the “main character” (I am using that as the name for the player-controlled character for this post. I’m still learning the correct terms.) will move around in a small 3D world (that has a very obvious entrance/gate to restricted area somewhere near the starting point) looking for collectibles. These collectibles may be coins, stars, or something else. I know that’s not important to decide what exactly they are right this moment. After “main character” has found all of the collectibles (let’s say 5 for the example), they can then go through the previously locked gate to a maze. They are then timed as they navigate it looking for the center. Once they find the center, they get their prize and the time is recorded along with their name.

Here is the point where I need your help:

I know myself, my shortcomings, and how to get myself to succeed. I know that if I just throw myself at this project, it will get about half way done, not anywhere near playable, and then it will sit on my hard drive until the bits rot out. So I need to plan this out. Storyboard it, if that is the correct phrasing. Have you figured out a generic or specific ordering of how to accomplish this, or come across someone else who has? Do I flesh out the details of game play on paper first so that I know exactly what the game will do from start to finish? How detailed should that be? Do I then move on to generic mechanics of the game using pre-built default characters and meshes and what not? Make sure it works the way I think it will then move on to character or level design, or do I do those first then figure out the mechanics? Does audio processing come last, or is that something that should come sooner? What are good “rules of thumb” that you’ve found out because you have worked on games long enough or you’ve heard from successful people in the industry?

I know a lot goes into games, these things aren’t made overnight and the best ones take preparation from teams of people. But I want to do it right and following good practices on a small scale will help me to finish what I start.

Thank you in advance for any advice or input you offer.