UDM2004

I'm playing my first season on MLBM 2015 trying to figure my way through but there are a few things I don't understand.

1. What does the abbreviation INF column mean?
2. What does the blue up arrow in the INF column mean?
3. Why do minor league players become angry when they are placed back in the minors after they leave the DL?
4. At the end of the season do I need to resign all of my minor league players?
5. Are my draft picks automatically given a minor league contract for the remainder of the season they are drafted in?
6. How many players should I have on my minor league roster (how many SP, MR, CL, C, 1B...)?

I'm sure I will have more questions the further I get into the game.

Thank you in advance for any help you can provide.