Earth is the most important element for me, but air is also needed, and all magic is needed in general, but the most important spells are: slow, haste, blind, lightning bolt, magic arrow. And, of course, something like meteor shower, explosion, portal stones, flight, but they usually appear towards the end of the game and usually ruin the whole balance.
Not all of them are necessary. There are almost no fire spells in your list. There are no good spells at all. Blind is useful only...