My recommendation, assemble the runtime hierarchy for your files, I.e., Textures folder, Pose folder, etc. Start Poser, reconstruct and apply your texture in the material room, then save as a material collection in your Materials folder.  Next, open your .Mtl file in a text editor of your choice, change Mtl Collection to Figure and resave as a .pz2 format.  Move this file into your Pose folder.

PNG's thumbnails are easy.  Within Poser, change your render settings dimension to 91x91 pixels and render your final scene.  Export the image into your Pose folder and name it exactly as your MatPose file.  In Photoshop or GIMP, open a rendered image of your scene, select the cropping tool, input 91x91 pixels in the dimension fields, highlight the area you would like to crop and hit ENTER.  Again, save out your PNG into the Pose folder with the identical name of the MATPose file.