Based on my experience from past years, they won't 100% of the time play as the tactic you set for them, however they seem to for the majority of the time. Things changed based on the score, time remaining, etc. However, still seems like it might be worth the time.
Yep—pairing all tactics with specific player instructions. Do they work as well as they should (defensive midfielders bombing forward)? Nope, but they work enough it seems.