So 500 vertices? that seams a bit small but could be good for practice
I know it's small, but that's just it.
A good Low poly designer is wat him makes special and good, because all the rest is just texture
You don't need to make all the special things and extras for a game, because means they need to render more, > more cpupower, > bla bla bla It's the art to stay low with the polys
But if you really want a higher value, than you say a number