aaaaaand to get the topic back on track!
Your coach is important as he trains your young players. Investing in a good trainer is a good idea to start off, but don't spend all your money doing it. $10000-$20000 should get you a level 4 trainer, and that's a great place to start. In the first season don't worry too much about his salary as you learn the game you'll make adjustments down the line. The higher the level trainer the better he is at improving your young player's skills, but 4 is more than fine for the first season or 2, as it'll be doubtful you'll be able to afford good enough young players to warrent a level 5 trianer or above.
Your PR manager and team doctor are less important, especially to start off with. You'll learn what they do as you go along, but for the time being stick to the level 1 ones you have already. You won't be hindered hardly by leaving them alone while you learn what they do.
Hope this helped!