Thanks for your replies

And now the extra question: when I snap fire with my hellhounds on some units that are engaging me in close combat, how many can I hit ? For weapons that do not use templates, that's quite easy to count the number of attack dice, but for a template weapon, that's a bit more confused.

On the other hand, in-game all of the movement would be happening simultaneously, not model by model, so it would be reasonable to have the attacker move all of the models relatively simultaneously (say, 1 to 2 cm at a time) so that an exact decision of when to fire the template(s) can be made.

An easier way to do that would be to say that when the attacker declares that a formation is moving to enter Close Combat with a defender's formation that has zero-range templates, then the defender places the templates on the board at that time (IE, before the attacker actually moves any models in the assaulting formation) and then the attacker must move into close combat using any route available. Any model that moves through a specific template takes an attack from that template, but only one possible attack per template regardless of distance moved through said template. Of course, the attacker would be required to complete the Charge to the declared formation. No declaring on a formation, making them use their Snap Fire, then doing something else.