no, you don't want only front scatter.  but back scatter is only relevant in very, very particular places, and even then, only very particular situations. if you're using it everywhere, your skin won't be at all accurate. not even a little.

no, Poser isn't able to have even simple SSS.  that spread carodan's talking about is absolutely crucial.  as is the blur of micro and macro features.  check out the papers on BSSRDF, like:

http://graphics.stanford.edu/papers/bssrdf/
http://graphics.ucsd.edu/~henrik/papers/skin_bssrdf/

at a distance, and low resolution, for things with a relatively low scattering radius and smaller scattering component than diffuse component, just colored diffuse and specular work.  and in some cases, Edge Blend (i think, at least that's what some very soft-looking skin textures/materials use).  but do a closeup, or make something like soft wax or gelatin that's almost all scattering, and you get a really flat, really problematic results (especially around the nose).  and the more bump and detail you have, the worse it looks.  it looks like painted wood or plastic. the best, most realistic Poser close-ups without postwork have this problem.  and that's just skin. 

there's a reason bagginsbill's candle shader required a geometry dependent fake, and couldn't react to light in general.  or that it's hard to make a white porcelain which is easily distinguished from equally shiny white paint.  for Poser, we've all come a long, long way.  but compared to even free renderers, we're just beginning to address realistic materials.