I think, until you get to the point that youâre ready for other eyes on it, you are actually your best resource for this and regardless of when itâs released youâll always be the most important. Whatever you do, it has to be something youâre willing to write, so I would focus on the overall story you want to tell (including the story of your protagonist) and any branches in there, and the style of game you want to make - then take some mental distance, step back from being the storyteller, and think as a player. What kind of characters would you want to make? If you were playing as a specific character, how would it change the tone of what youâre reading? What choices would that character make? What kinds of different stories could that character have?
The stronger your vision for your game, the easier this question will be to answer for yourself because the character customization, stat system and player choices will live side by side with it, feeding into and making each other stronger.
These are, of course, all hypotheticals but as an example - letâs say you wanted to make a game about a doctor in an apocalypse with themes of loss and grief and the doctor PC being unable to stop those cycles, you probably wouldnât care to have a stat system that focuses on a million different combat stats because that distracts from the point and game youâre trying to make. You might have one or two combat skills and a few other stats that focus more on the emotions, personality, and medical abilities of the PC. And your story branches might follow a similar path. Maybe thereâs a tense situation that will split PCs on different paths where some of them become apathetic and others the exact opposite, and maybe thereâs some that stay the same.
Just an example. If you wanted something more gamey and less character driven, you could of course do that too, again it all just comes down to what you actually want to do and say. Like maybe you wanted to write a gamey sci-fi story about an intergalactic game of tag for the prize of a billion dollars, most of your stats and choices would probably be more so about the PCâs physical abilities and how they play the game and the PC may or may not have a character arc at all, depending on how you want the story to be.
TLDR; Thereâs not really a right, wrong or specific answer to give here. And there are no rules. The story branches, PC customization and development (if any), and the stat system (if any) live side by side with your overall vision so you can come up with any of them first but ideally they would all make sense together in the end. Also, best of wishes on your writing!