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.

Unless stated otherwise, such spells are not cumulative and casting them multiple times will have no further effect.

No. A roll of a natural double 1 isn't merely a failed Casting roll, it is a Miscast, as described on page 109.

No, your casting result determines the 'strength' of the spell. In other words, the higher your casting result, the more power the spell will have and the greater its effect will be.

As stated on page 111, in order to dispel a Remains in Play spell during your Conjuration sub-phase, you must beat the minimum casting value given in the spell's description. This is the case even if the spell was cast at the higher of two given casting values.

As many as you wish, or, perhaps more accurately, as many as your opponent has in play and as many as you are able.

It ends immediately.

Yes.

If the Wizard is within range of the model casting the Bound spell and not otherwise prevented from attempting a Wizardly dispel, yes. As stated on page 109, you may attempt to dispel a Bound spell as usual.

Yes. Whilst such attributes are as protective as a suit of armour, such models do not wear armour.

They only need to be within the fighting rank.

Yes.

Yes. Magical vortexes are considered tall enough to affect even models that are flying high above the battlefield.