You are falling into the caterpillar's dilemma; there's too much to control, so it seems that there is no way to control it all, when the answer is simple -- Don't bother.
Think of the Borg Queen (or any 'lead' Borg) as the brain, specifically, the Super-ego. It's the part that does the 'conscious' thinking, and decides on major courses of action. The individual borgs, on the other hand, have very little volition (in that they have no overreaching goals), but they do control individual details. Much the way you don't usually THINK about breathing, the Borg Queen doesn't have to think about the mini tasks required to keep the ship running; in your case, your brain (and spinal cord, hypothalamus.. gah.. not going to get into the biology here...) keeps it running on 'automatic' without your conscious intervention. Need to increase the o2 level due to a heavy work out? It happens. Need to contract vessels and keep heat in the body? No problem.
Many (although not all) of those functions you can consciously override (and the ones you can't, you can often influence by other behaviors), but you don't normally bother. Think of the Borg collective as a body (or, rather, the shared parts of their brains -- think 'distributed computing')... And it functions much the way a human body does.
(This is also one of the reasons the Federation away teams could beam on-board and explore without being attacked; the units they encountered had jobs to do, and worrying about what others are doing (or if the others are Borg) was not one of their jobs. It's possible there were internal security Borg, but we didn't see them, and they would most likely be very rarely called upon, and possibly left in storage/stasis most of the time.)
They DO have an ability to do something your body can't; at need, problems can be passed down the line to let them all 'think' about them. They only do this when directed to 'from above', but when they do it, it gives them massive processing power.