I’m new to SP but old to Blender; this is what I’ve learned in the last few days:
fbx works better in SP than obj - the ID map options
It’s better to not only apply all transforms in Object mode in Blender, but to join everything with one UV map and a clean set of materials before exporting.
That meant saving my Blender file to something like “ModelForSP.blend” and making some changes:
Apply all transforms
Explode any parts that are covering each other
Fix the UV maps in such a way that you can split them back later if you need to:
no overlapping faces, unless they’re mirrors and you’re OK with that
I arranged them in 4 quadrants on the UV map, worked fine splitting them later in PS
Merge duplicate verts.
Clean up the file
Use multires modifier to make the high poly version if you don’t already have one
*_low poly with “apply modifiers” unchecked
*_high poly with “apply modifiers” checked
Export to fbx as you mention above.
All this work totally worth it - I had the thing textured in SP in about half the time as anything I’ve done before, and it came out better. Those smart materials are genius. Also the brushes. And that was with me barely figuring out how to do it. After I had my materials exported from SP and split in PS, I brought them back into my first Blender file so I could make the collada export I actually needed,