Had the same concerns when I was deployed.
Couple of points - unit SOP may screw this up, but I found that a decent concealable holster kept a lot of folks from knowing I was armed. Surprising the bad guys is always a good thing. I used a yaqui slide and was rarely made in ACUs. The slide compressed enough to be comfortable when I had my IBA on. When my IBA was on, the M9 was on the IBA.
Obviously, always keep a round chambered.
Test your M9 magazines extensively. Don't marry them, if one chokes, kill it and get a new one.
Carry a knife that you can access with your weak hand. I preferred a 3 or 4 inch fixed blade on my belt, next to my spare magazines. A good spot for additional magazines or a folding knife is the ankle/calf pockets on your ACUs.
Keep a decent amount of loaded mags on your person and more on your IBA. My thought was to always have a fighting load on my person and used the IBA for more goodies and novelties.
I wanted to be able to fight even if I dropped the IBA or was on the FOB without it handy. I kept 5 magazines on my person, a good knife and a improvised tourniquet.
As far as the drill itself, the shoot from the hip may be necessary, though I train a much more on firing from step two of the four count draw. Puts your pistol in a better spot. If your firing from the hip, your probably rolling around on the ground. To train this safely, bring your weak hand up and hold it in a block position next to the ear on that side.
FWIW, we had a kidnapping attempt in our unit. The bad guys tried to knockout their target by hitting him in the head with a rock, darn near worked.