Hey, very interesting idea actually
But actually, animals with many legs usually have puny legs. Even if you were to invent your own creatures, more legs always means less space for legs, which means smaller legs.
So, a way to solve the issue would be to also take the mass of the feet into account, since kicking with a tiny leg is pretty much futile.
(Unless, the creature were to kick with many of its legs at once... Could it do that? Let's take the creature's balance into consideration...
And you already mention musculature and body mass... how many independent variables would it take to functionally define a creature? Pokemon, in its apparent simplicity, probably takes about a hundred already (name, level, rarity, personality, base/actual stats, actual/learned/compatible moves...)
Obviously the abstraction has to stop at some point! Else one ends up with 3D data-points of each creature's body part's mass and volume.