Get a fuly upgraded Training Hall and 4xlevel 20 coaches (don't bother getting the Special Teams coach as it isn't worth it for 1-2 player(s)).

PS. I am assuming that your stadium includes all the VIP and Executive seats possible to build.

And plan the build so it finishes on a Thursday. That way you don't have to pay maintenance for that week, but still get training bonus the Friday next day

Which means you should hire the coaches on the same Thursday the build finishes

My 2 cents:

I builded my training hall as I had at least one player which was capped on the physical skills. Not before, just to have it.

I then added my coaches for offense and defense, not more.
With this coaches I was able to train most of the primary skills I needed.
At that time most of my players were still in the "physical training" program, so only a few needed the other coaches.

Next step was getting the training hall extensions.

I made some mistakes, like buying and hiring before wednesday, but I think a saved a lot of money buy keeping my staff small and hiring only then the next bunch of 20 coaches when I needed it, like a season later.