I will also play as solo four players but my variant is I will allow a time limit, usually 10 minutes (no cd) to allow me to plan out all my actions for each player.
This is really intriguing. Do you look up the threats for the mission, reveal them, and then begin playing as the first character? Do you play your cards facedown using this variant? That would make for a real challenge, I'd think.
One of the pros for this game for me is the short playtime and the atmosphere created by the soundtrack, but I'd be interested to try your variant sometime.