I've heard people say how on their game certain players stats are wildly different by contrast, so I think it is completely randomized, with the possible addition of a better chance of good coaching stats/staff stats if the player was especially good at something as a player. I say that because I have noticed a lot of brilliant players showing great talent for their area of expertise, world class defenders being great at defensive coaching but not a lot else for instance.
There is also training of coaches however; I've taken on a few of my players who had retired when their stats were pretty average and they have developed into some of the best in the world. The only stats I should add which seemed to improve though are the actual coaching areas such as attacking, mental, technical etc. All of the key ones universally such as determination, man management, motivation I've not noticed move up at all, with one staff member actually showing a drop in determination somehow despite us winning everything.
If you've already got all the coaching staff you need to cover the areas you're happy with, I'd promote taking a chance on a player you like with some workable stats which aren't disasterous...they might improve to the point where they'll be a longterm employee for you.