The model is armed with an arquebus or similar musket-type firearm. The arquebusier may fire a ranged attack at +2 over Long Range, at +1 over 2 x Long, and at no modifier over 3 x Long. These modifiers include a +2 bonus for the weapon's accuracy and a halving of the range modifiers. Add the shooter's Combat score as usual."
This is the trait vs description conundrum again. Given that this is the rule description, we should probably cap it up to match "Arbalest" on the preceding page and "Arquebus" in the subsequent paragraphs.
The model may be part of an Artillery crew. Firing and moving an artillery piece is a Task, and only models with the Artillerist rule may take part in such a Task. In general, you'll roll dice for all the members of the artillery crew, total them, and use them to accomplish the task. For further details, see Artillery rules.
The cost of the Artillerist Trait does not include the cost of the weapon itself, which must be paid for separately. Technically, a single Artillerist has all the skills needed to operate the weapon, but the high cost in Task points will mean that an under crewed weapon will take several turns to be reloaded. Large artillery pieces are outside the scope of a skirmish ruleset. As a rule of thumb, they would also require a minimum crew to be manhandled."
I'd suggest capitalising "Artillerist" and keeping "artillery" in lower case throughout, to reflect the distinction between a game trait and a general term.