For game shape reasons, it's ideal to get every player on your team at least 48 minutes a week, and less than 75 or so. I find that a roster of 12-13 players is just about right for this, and I'd recommend trying that out to start.
For your training program, you could train 3 players at a single position (such as PG, for example). Many people do this, as it trains individual players the fastest. If you train 5 players at 2 positions (such as PG/SG), you have a bit more flexibility, and I prefer training 2 positions myself. The draft is happening next Monday, and who you draft may influence what training program you decide to create. I recommend not spending much money on potential trainees until after the draft, so you know for sure what you have going into the new season.
For your staff, having a level 4 doctor, trainer, and PR manager is good to start; I think the level 5 trainers are a bit expensive for brand new teams. Once you have been running your team for awhile, and definately have some extra money to spend, then I would look to get a level 5 trainer.
Good luck with your team :)