What I was planning on doing is let every exec (owner, coach, gm) write their own philosophy, what they're looking for in a team, that kind of stuff. Then I'd let the owners hire their GMs and coaches. If you absolutely want to be with a particular GM, you can always team up with that person and try to get hired by the same owner.
How much time? Well that depends on how much time you take to do the lineups & depth charts, send them to me and re-assign rosters when needed. Plus, of course, keeping informed about the league. Some like to do their lineups based on ratings, other based on stats... it doesn't take the same amount of time for everybody, so only you can answer that part of the question
As to sims... I was thinking once a week, 2-3 weeks per sim, though that could change anytime, it all depends on what you guys want.