I have to say, lowpoly is an art, nothing but big respect to anyone who can master it.
Not sure what I'll make with this model but I'd like to try and make a new one, somewhere closer to those specs you gave me.

@Xpand
Are there limits on models for BNG apart from it must be 1 mesh, 1 material, one texture?
I know that model must be exported as triangles but not sure I noticed a specific option in Blender.
What would happen if model wasnt exported as triangles or had more materials on it?