Let's not expand to tactics here but to talk about players/positions and tactics.
Ok, DMC is also a key player for me.
I 've seen a lot of times players with only DMC position and to be honest, I prefer to have another player with worst characteristics but double position like DC-DMC.
I wish the game could offer players like DMC-MC - at least in scout list or recommended players.
I never seen so far (I 've seen in recommendations MC-AMC), so I build one DMC-MC with greens.
Even better is one DC-DMC-MC. Perfect for rotation and back-up.

Midf players
Not much to say about them.
I just like the idea to have the C-K sa and to set them in corner-kicks so to have my other attackers (ST and wingers) in the GK area.
I avoid to buy MR - ML as I 'm searching for MR-AMR and ML-AML.