"Ackerman" refers to the pivot point of the hinge relative to the position of the control horn's tip (where the control wire or rod is attached). Neutral would be with the tip exactly over the hinge point, negative and positive (I forget which is which) would be forward or behind the hinge point. Ackerman controls how much constant tension, or development of slack or increasing tension occurs in the control wires during control movement. You definitely do NOT want increasing tension, as it strains both the servos and mounting points of the control horns on the surfaces. Some slack on a slower flying plane with a large control surface is fine. The slack will develop on the "push" side of the control, as air pressure on the control surface will hold the "pull" wire in tension. A fast plane or one with a smaller control surface will develop flutter more quickly with increasing slack in the wires.

I've used a pull-pull setup once on an elevator system once, with great result. I did it primarily for scale detail, as it was a WWI plane (Bristol M-1). I used a single servo and bell-cranked it to a horizontal rod which had 2 arms, one for each pair of top and bottom wires. My elevator halves are tied together with a central rod, so if any one wire were to break, there is redundant control.

Like Rodney mentioned, I ran my wires through tubes to the exit points on the fuse. I used neutral Ackerman, and ensured all the tubes and pathways were symmetrical. this model was sort of a testbed for what I wanted to do on my later, larger scale WWI planes. The beauty of using the bellcrank and rod is that you can place the servo way up front if needed for balance, and run the rod back to the horizontal control, which allows you to shorten the runs of the control wires in the pull-pull setup. This can be for convenience of linkage location, and shorter wires are easier to maintain in adjustment for tension.

In the interior pics, you can see both the rudder pull-pull wires and the elevator pull-pull with the bellcrank arm to the servo, and the wires entering the tubes. I used coated leader line of about 25 pound test for my wires. This plane is 1/6 scale; I'll use at least 50 pound test for a 1/4 scale model.