I was under the impression the further up the tournie ladder you went the more tanks you were allowed the field, so the final match was supposed to be a full scale skirmish except their academy could only afford the 7 or 8 tanks or whatever. The thing is, you don't need to know anything to have interesting tank battles in the same way I don't need to know the in and out intricacies of soccer to be excited watching a decent match. And 'offside' rules or property destruction limits would feel out of place in Tankery, which is apparently meant to emulate as much as possible an actual battlefield (although they do seem to avoid gratuitous property damage, probably just because it's inefficient).
As for the cell phones... I don't know. I assume it was fine because they only contacted within the tank crews to relay commands. That should probably go to a review board though. :3
Watching the episode again, Katushya's initial firepower stormtrooper burst looks like it's meant to herd them towards her pincer arm, but the Student Council tank draws a lot of their firepower as it charges and lets the rest break through around them. If you imagine the bulk of her forces covering the 'weak point' and her stormtrooper guard struggling to reload and re-aim at targets not heading for the place you predicted at the same time, it becomes a lot more understandable.