To your first question, I chose post-Maderame Joker for the simple reason that I haven't actually played past that story arc, yet have read the majority of the manga series. I decided that it would be a good place to take him from as it would be a good place of reference so as to not have to struggle with that much of the past storyline of the Palaces, making for more room for growth without past experiences getting in the way of decisionmaking. In my opinion, the manga iteration portrays Joker with a more concrete personality along with a slightly altered frame of storyline, which I thought would be more fit for an RP setting. Of course, it also doesn't portray him as a one-man army as the Wild Card could give off.

An interesting thing about the Wild Card actually that in the manga iteration of Persona 5, Akira doesn't actually show any reference or capability of the Wild Card, and the only Persona used by him is Arsene, used as an actual aid in battle as opposed to the game using the persona as a skillset.