I’m sorry but this sounds like a terrible way to design a game system.Basically think of every TTRPG you can, strip it down to it's core principles, and combine them.
You've got all the ability to create as much as you want as both GM and player, and this is done quite masterfully with creation charts. Basically, if you want to make a custom race, there's a chart for it. And it's completely up to you how you interpret these charts. Literally says it in the book.