What needs to be added to quinoa flour make it "behave" like all-purpose flour?
Quinoa and Amaranth are from the same family and are quite similar in makeup and constitution. You’ll probably want to add some stabilizers and extra binding power to make up for the lack of gluten.

This recipe for amaranth bread adds rice flour, tapioca starch, arrowroot, and xanthan gum - which in my opinion is a bit of overkill. I would probably stick with just agar-agar for the mouthfeel, egg yolk for extra binding and xantham only if it’s too crumbly.

And on a side note, lightly toasted quinoa with bittersweet cocoa powder is a great (and classical if not downright tasty) addition to your breads. Good luck