Can I add my own .PMX files? Are Jiggle Bones supported?
No,sorry,you still need manually convert .PMX to unity animation（use mmd4mecanim) then converted to .anim use my unity plugin,which I would like to upload today,if everything works.
Jiggle bones should map to spring bones in VRM.
Here is some link I found how to covert mmd avatar to vrm format: