I always keep them at 10, and I had 6 units. Another popular size is 13, because then you only need to take a panic test when you take 4 casualties instead of 3, but it makes them slightly less maneuverable. On redirecting, the trick is to put your crappy unit directly in front (like 1 inch) of the unit you want to redirect. Then you put your unit at an angle, facing away from where they want to go. This makes it so they can't charge anything but that unit, they are only allowed one wheel on the charge and they can't hit any other enemy units while charging. So you force them to fight the skinks (who are very dead from that point, but it's sometimes worth it). The reason you put them in an angle is for your opponent to make the overrun or pursue move bad, as it will make them run in the angle you would like them to (which presumably is bad for them). They will probably elect to reform and stay put, but if they are frenzied they can't, and they can still fail the restrain test. The enemy unit then stays in place, giving you often two turns of time. And indeed, your TG unit will be worth a massive amount of points, if your Slann dies you probably die, so don't let that happen if you can!