Looking at your combination-spells. This was done in Septerra Core to some extent. You won "cards" through the game, each with it's own magical ability. You could use up to three cards in any one spell. Most combinations were legal, although some conflicting ones were banned (eg. Fire & Water, Fast & Slow).
Your idea could work if a lot of planning was put into the component spells. I would not include Charm as being charmed by a searing ball of fire doesn't make sense. What about a Hypnotism spell? Area Effect should be a spell of it's own. And combination magic should exponentially increase the amount of mana required to cast it. Some combinations (thinking in D&D terms):
Hypnotism = Charm
Hypnotism + Fire = Fire damage with no Reflex save (ie. can't dodge the attack)
Fire + Ice = Wall of steam (can't see through it)
Stun + Fire = Knocked out by blast
Fire + Blast (Area Effect) = Fire ball
These are just some of my thoughts. What other component spells could there be?
