1) Absolutely not. Not only would this encourage powergaming, I feel it is inappropriate.
2) Magic is elemental in nature in this world and I don't want to open the door beyond it at the moment. Definitely no spells of that nature are ones I would like to engage in.
3) They are a classification to describe the concept of how they use their magic and seen by the magical community. But yes, artifcem magum are definitely individuals that utilize their magic through their items -- whatever foci they may be. There would be nothing of the matter similar to a shrink ray or conventional firearms however given that even with magic the civilization of Iquenos is still mired in a sort of Imperial/Renaissance/Late Middle Ages era which means essentially that there are cannons and medieval long guns or blunderbuss-esque devices.
4) Your element is your biology, so yes, there is only one per character due to the makeup.
5) Storm. Shock. Lightning.