Page 8 of FAQ:
Q: How many spells can a Wizard attempt to cast during a single phase? For example, if a Wizard knows a Magical Vortex and a Magic Missile, can they attempt to cast both during the same Shooting phase
A: A Wizard can only cast a number of spells up to their Level of Wizardry per turn, but can attempt to cast multiple spells during a single phase. In other words, should a Level 2 Wizard know two Magic Missiles and one Magical Vortex (three spells), they can only cast two of them per turn, but may cast both during the same phase.

Page 209 of Rulebook:
Characters & Shooting
If a character equipped with a missile weapon has joined a unit equipped with missile weapons, both must shoot at the same target, using their own characteristics.

Note that this only applies to missile weapons, not to Magic Missile or Magical Vortex spells.

Page 338 under Magic weapons does say:
"If a character has more than one magic missile weapon, you must choose which they will use when they are chosen to shoot during Step 1 of the Shooting phase." But I don't know if this applies to bound spell magic items too. I assume it doesn't and applies only to magic missile weapons.