So, it looks like it's time for some reminders and updates on the conversion processes and where we stand.
Right now you just can't use V4, G1 or G2 skins on G3F. I don't know if this will change. Given the new UV and material setup, probably not. People on the forum have been using a lengthy workaround involving converting the actual textures. I can't say that I recommend that, but feel free to try it.
Expressions will not transfer in either direction. G2F's face is animated with morphs, whereas G3F's is animated using a full bone rig; they're just not compatible setting types. You can see G3F's facial bone rig by using the "show hidden nodes" option in the scene tab, but don't do it unless you really need to; there are many, many small bones there. My brief experimentation with morph transfer did not give good results in the eye area or with JCM transfer.
You can convert V4 and G1 clothes to G3 using