Since you're learning and admit as much now, I'll help you.
If you're counting on your BL players to develop, you're doing something wrong. For the most part, 4th year pros are largely done with development. If you have a bunch of 2nd/3rd year pros on your BL roster, you need to re-evaluate your roster-building methods. Coaches will help slow decline of learned skills but you're looking at low 30s for positions and mid 30s for pitchers. If your team is loaded up with old guys, you need better coaches OR you need to re-evaluate your roster-building methods. Finally, if you're fretting over a primary rating of 63 over 58 with coaches, you're making yourself miserable for no reason. The "important" coaches, IMO, are fielding coaches. They affect your entire organization.