"I sometimes struggle with textures" everyone does, even top modelers because you there is so much that can be added, but its about the trade off, if I spend x amount of time adding this detail or that detail, how much will it really be noticed? or will someone not notice it there, but notice if its gone? some times its even hard to think of details to add that that becomes an issue as well.

as far as the polys, you dont necessarily need to add polys to do it (i will look better if you do tho) but the hair needs some geometry.either do some shifting, or add about 40-50 polys worth of hair to the characters and they will look fine from the point of geometry.