Team Depth

You typically want at least 1 backup for each position in franchise (except kicker and punter)

If you're running a 4-3 defense you need at least 2 starting DTs - I also keep 2 backups. If one is a run stuffing DT that isnt great at pass rush then I'll have 3 starting level DTs and move the run stuffer out of the depth chart in the "RDT" position. 

For CBs, you need at least 2 starters that can play outside and a 3rd that can play in the slot in nickel formations. I usually have 3 backups behind them.

For O line - I always carry a backup at each position on the line. You can leave out the backup center and use one of your backup guards for that if you want to free up a roster spot for other position depth.