Any suggestions for the LOWEST settings I can get away with and still have it look okay? It doesn't have to be Pixar quality.

I don't animate with Poser. But, just based on what little I know:

Lower pixel sample size to between 3 and 5. (5 would be the max, I'd think. There's rarely any reason to go above that for most renders, IMO.)

Shading Rate at .2 is fine, won't really matter.

Use fake Subsurface Scattering. So, turn SSS rendering off. There are several texture sets and material settings out there that do a decent job of it that can still be used in dynamic situations. (Where the light/figure is moving.)

Shadows on.

Set displacement to 0, so it will rely on material settings and you can better control it. (Shouldn't matter much, so you may not have any displacement.)

Smooth Polys - On. (Doesn't really matter at all in terms of performance, but if you have inorganic objects not especially constructed for rendering in Poser, you may have to go back and adjust their Object options to reduce/eliminate smooth-shading effects if you see their geometry get really warped when they're rendered. Just turning off Smooth Polygons for individual objects, without adjusting their Crease Angle, as well, will often not solve the issue, since those are sort of separate things in Poser, I think.)

For the rest, the biggest hogs are going to be the Sample size for various settings, their Cache settings and Bounces that are calc'd.

Use a Guassian filter set at 2, no Tone Mapping and Gamma Correction at 1.3 to 1.8 for PC and higher for Mac. (2.2 for Mac, I think.) You'll have to fuss around with settings for IDL intensity, depending on if you want that in your scene. But, if you don't want it, you'd save a lot of time by unchecking it and "faking" it with other lights.

On your lighting: You will likely get better control of your lighting and much less render time by choosing "Constant" or, at the very least, "Inverse Linear" lighting under the Light Option panel for individual lights. However, you will likely get even better render performance if you just use an IBL and one Spot, to bring out certain Material channel features that IBL can't interact with. (Spec, etc..)

Fuss around with your Shadow types, Ray or Depth Map, and their settings. Lower Blur Radius is faster, but may not be as realistic, depending upon your setup. Minimum Bias shouldn't be any lower than .6 or so, IMO. But, I'm no lighting expert. You'll have to balance the "look" of your lighting with your rendering performance.

In animation, you can cut some corners, so cut all of them that you can and fake the rest. :)

PS - I don't animate with Poser and don't even render very often, either. :) But, hey, it's just a few suggestions to help you get started.