I only play with the DL on Defense. I pick either the guy in front of the center or closet to the center.
If the CPU is getting long blocks on passing then I switch to a defender closest to the QB to speed up the throw.
For Fast Coach progression being on is a must in my opinion. Here is why.
The Team upgrades will make the CPU give you a better game. You will notice how much better even the bad teams play about halfway through your second season. It also helps the CPU to unlock their extra 3 slots faster helping them. Since the CPU is not smart like the Player is to know which ones to go for first. They need all the help they can get