Your dark section always seems to be a bit tight in circumference, considering it's just the side away from the sun and not a smaller planet obstructing the sun's light. Anyone else feel that way or am I nuts?
Yes.
Any planet would practically have a 1:1 terminator. That sort of lighting implies an almost infinitely large circumference of the star, which is unlikely for any planet that stays solid, and especially a (water) ice planet.
I mean yeah if you had a planet orbiting something like Antares at relatively low orbit, you could have large aberration from half lit, half dark division, but that would likely be a special case of special case.
Detail for a snowball is very hard to do with just surface texture. If you put significant amount of detail in it, it'll just lose it's albedo and won't look very snowy any more. What you can do is acquire some height/normal map, make a rather bright surface texture, and render it in 3D modeling program with the height map creating surface elevation lighting for the planet, which would likely be the only really visible detail in a planet like this.
Snow is, after all, rather white.
Another thing is clouds; you'll want them as well, as they will cast shadows to the surface and they themselves can be bump/normal/heightmapped to enhance the detail on the cloud coverage itself as well.
