With regard to AI teams - we operate a caretaker system. We have several coaches who have proved their value who take over un-owned teams using a second account during season end to ensure they don't get cap busted. The caretaker then handles the draft for that team to set them up for a new owner. Caretakers must be from the other conference to the one their assigned team is in.
From experience, we only recruit new players between pre-season 1 and season week 6. Outside of that window the turnover rate is too high.
We're in the playoffs of our 4th season, have 1 AI team right now having had 45 coaches in the league over those 4 seasons.