Coaches help develop players and does not actually affect the outcome of a game, except maybe the bench coach in the minor leagues and occasionally the 3B coach in the ML. Therefore the understanding of the coaches may be a good idea.
One of the first things one does after the Budget is set, is to rehire previous coaches. Not all coaches will want to stay and you may decide which ones of the returning coaches you want to keep and ones you need to let go. Don't count out coaches that do not want to return, you can offer them a contract in the hiring phase, sometimes they will return for less money than a higher bidding team even.
What makes a good coach has a different perspective from various people. Each coach has a primary stat associated with the type of coach he is. For instance a Hitting Coach has high hitting IQ. Some of a coaches other IQ ratings however does help in developing players throughout an organization however. Which coach to try and hire and try to out bid everyone else is your choice. I equate the coach hiring phase as a dog-eat-dog Free Agency quandary.
The coaches you hire at the ML level should equate to your players. IMO, the coaches you want to hire depends on the age of your players. If you have several players still developing at the ML level, then you may want coaches with a higher patience rating than discipline, but you still will want both high if possible. Remember that the highest one in these two areas override the other for the most part. One thing in the Players Guide they mention is that a Hitting Coach is helped by the Base Coaches in developing players at the ML level. I had to scratch my head at this one for a while to understand their meaning behind this. Then it dawned on me that they are right, a players base running ability is a hitting rating.
The Bench Coach at the ML level used to be one of the most sought after positions of any coach and every owner. However we are led to believe that the ML Bench Coach really has very little impact at the ML level unless you get tossed from the game. That in itself is not the easiest thing to do, I think my record for doing that in a season is about 15 and I was trying hard.
The Base Coaches teach base running skills to the players. You would think they could affect the outcome of a game somewhat by sending runners especially at 3B, but they say no. I try to have my best coach at 3B just in case.
Pitching Coaches deal with all pitchers, one for the starters and one for the pen. Here again age could play a factor in what type of coach to hire for each.
Hitting Coaches deal with your hitters of course.
The ML Fielding Instructor plays a major role at each level in the organization. His abilities affect glove development at all levels and all players. A high glove, patience and discipline are optimal here at least to be successful. It is however better for this type of coach to have all attributes as high as possible.
At the Minor League level, coaches work almost the same way but their duties are more encompassing with less pay, hmm that sounds familiar. Most try to develop a stair step approach with coaches, meaning the coaching gets better as you go up the ladder. Some like to set one level, usually AA, with good coaches and put the best young players at that level. Either way works in my books. But what to remember about the coaches is that they need to have a high patience for players to develop. That doesn't mean one with a low patience should be over looked. I have had success with low patience and high discipline also. Another thing is the Bench Coach becomes more important at this level. You will want his abilities higher in all aspects if it can be done.