You can get away with a lvl 1 PR manager but it will hurt you slightly in terms of merchandising revenue.
I would highly recommend against a lvl 1 doctor. Having a lower lvl doctor increases your chances of injuries in games. There is no point having a great trainee only to have them injured due to you not having the doctors to prevent injury.
In general, I would not recommend Aussie D4 teams get lvl 5 trainers at the expense of other staff. You are much better off with a lvl 4 trainer and boosting the lvls of your doctor and PR manager