How to decimate mesh to work out for printing?
Well, since I just did this, I would say, decimate it to a reasonable level, but not so much that you lose detail. Unless you have error messages from your slicing program, you should be okay. 3D printing doesn’t require your model to be as low poly as would animation. If your printer has some sort of limit, follow that, but I don’t know of any limits. The slicing program is converting the model into image slices, so I don’t think there is a face limit, unless it chokes your computer.
In my case, I had a lot of coplanar polygons, so I was able to reduce the face count quite a bit without loss of detail.