1) I would focus on upgrading your guards, because your inside rating seem pretty good (thanks to guerrero, launay, and maulela).
2) Both, but it seems like you're selling out your LT, CS, and LB, so you should raise those prices. And you should also raise your bleacher prices a little. When you promote, you get a big boost in attendance. (At least I did.) If you need to save money to buy better players, instead of building your arena, increase the prices a little. (Remember, you should not be selling out all of your games.) When you buy players, be patient to get a good deal, and I wouldn't buy anyone over 31 if you're looking to succeed in the long run without having to do too much rearranging.
3) Depends what level your staff is. You've got pretty good trainees in Smith, Sadler, and Guerrero, so your trainer should be advanced, but this is not a priority (don't go past advanced, and don't buy an advanced trainer with a salary over 20k). A good doctor is useful as well, but again, dont go past advanced. PR Manager is not necessary and would be the last priority, but he does increase your sales (again, dont go past advanced.)
I cant see Sadler's skills, but his height makes him a possibility for a PF trainee (Tall players train faster in big men skills and slower in guard skills.) Smith is 6'5, which is good for guard and SF, but if you want to train your top three trainees together, you could use single-position training focusing on big-men skills, occasionally switching to guard skills.)
Any players with a salary in the 5k range (at the start of the next season) will not be very effective in DIV, but they could be your role players/garbage boys.