If a 20-22 year old players rating stands in the 60’s but shows their potential rating to be in the high 80’s or 90 is it best to leave him in the minors to develop or bring him to the big leagues to develop? Which will make him reach his peak quicker?

The better coaching is usually better, however, are you prepared to give him major league ABs for 3-4 seasons until he reaches potential while he's hurting the major league team with his performance?

My rule is that I call players up regardless of age when they are my best option for that position. The one you don't want to do is call a prospect up and have them rot on the bench.

Various philosophies on this. I tend to move my players up a level each season, making exceptions for exceptional players. Remember that a player stops progressing once reaching the age-27 season. Some owners will focus on hiring the best coaches for the AAA or AA levels and just leaving players there until they think they are ready to come up (I like them to be around 70 overall, depending on position or where their key ratings are at). But make sure the prospects are getting playing time, especially over non-prospects.

Assuming your coaching gets better progressively at each level, I move my highest potential players up as far as they can go and still be a starter.