regarding staff this is my opinion,
for a coach, its either level 1 or level 5 and above, training is about commitment and improving your players should be given a really big attention. the training results is already slower than the pass few seasons, i know its hard to be in a bidding war but this should be the way to go. because level 4 and below doesnt give much in return.
for PR manager, the only reward you will be getting from this guy is a slow or a gradual increase in your merchandise sales, but from my experience the increase usually doesnt really pay off from what your paying him for his salary you will realize whatever increase your getting is just the amount your paying him for his salary or even more.
* my personal advice is, the PR guy is just a support guy to your team. your overall attendance and money making ability rest on your team entirely. if you are sure your team can make a good run at a season just get a level 3-4 guy for division 1 teams which i recommend try getting with ability
for ability this is what i do:
1) if you think your team can mostly win your home games try getting the national affect since it will help you more on the road
2) if you think your team is just an average which you feel you cant win consistently get the home crowd guy, it will help you on your home turf, its better this way you lose more money through attendance when you lose at home.
for lower division team i suggest just getting a level 2-4 guy same with ability.the only good thing also having a high level PR guy is when you lose one game it helps lessen the after effects of losing n your home game attendance but again if your cutting in below or even just a little above .500 winning % i think your just wasting money.
for a doctor
i would always recommend getting at least level 5, its ok even without ability. but overall for me injuries happen at random affected by a number of factors, but to help prevent injuries is to know how to balance your players GS and minutes played ( i havent experience a injury since season 4 till last season wherein i wasnt active and most of my starters played heavy minutes and GS affected ). but the doctor helps lessen your chances to get injured even if your player get hurt.
this is just me, because i havent proven much that injuries also happen on the matchup setup or so ( im not going to start )
hope this helps