All right, after a bit of discussing, it's unfortunate but we have to say "no" on all three questions. They all sound interesting, but due to game mechanics both for Empatheias and the Persona games themselves, it can't be done.

However, if Philemon were to ever app into the game, this could be a completely different story. For instance, perhaps the original Velvet Room may not be accessible, but either some part or a new version of it could be made for Empatheias universe. The same goes with non-Persona characters learning Personas. If characters who have the powers to create Personas, like Philemon, were in game, then it would be doable.

But since Eikichi doesn't have any of these abilities, it cannot be done.