I think in this case it could make sense to build some kind of 3D to 2D pipeline to speed up the process. For instance, have a look here: How to make a 2D isometric spritesheet from a 3D model using Blender | OpenGameArt.org

Sounds intriguing.

There is also a bit of a hacky but somewhat functional trick to geneate forward-left/right and backward-left/right from forward and backwards sprites.

"A turn around sheet should show a character from a variety of different angles. The most basic are forward, backward, left and right, with the 3/4s angles forward-left, forward-right, backward-left and backward-right creating a more complete set. Left and right can be flipped versions of each other unless a character is asymmetrical (for example, wearing an eye-patch or having a facial scar). Backwards can usually be made by editing the forward facing sprite by covering the face with hair (or bald head) and reversing the hands and feet. Finally, the 3/4s angles can be made from the forward or backward image by using the 3D translation option in GIMP, rotating it by 45 degrees on the Y axis. This produces a reasonable albeit flat looking facsimile, although it is often best to then stretch the height back down by a bit. A degree of depth may then be restored by layering the image over itself offset by one or two pixels a few times. The 3/4s left and right can again be flipped provided the character is symmetrical."

This allows you to only produce five or even three frames for each direction. It might not be the best to use for the base, but might work for some of the overlays?