Magicka styled spell casting

[Sada]

Hey everyone i'm thinking of developing a spell system for EO similar to the one used in the game magicka (but ofcourse target based rather than aiming). For those of you who haven't played magicka i'll give a quick rundown of what they do.
You are given access to multiple elements (Water, fire, rock, electricity etc etc), with these elements you can put them together in different combos to create different types of spells then you can choose to either use it in aoe, on your sword for your next attack, self cast or just aim it.
different elements don't work together such as electricity and rock, they cancel each other out.
Some elements such as fire and water mix to make hidden elements like steam.

So in this topic I wish to discuss the design aspects and ways you would personally go about coding something like this in regards to the EO engine.

The things which come to mind are perhaps an array of size 5 (more or less depending on the amount of elements used) which gets filled up with different element ID's (which would take up spell slots) as you add the element to the combination.
The current spell system could still exist with some tweaks (such as self cast damaging spells and the ability to change features of a spell depending on it's form, eg, aoe, self cast etc)
then you would need to have a giant list of different spell combinations which rather than being spells learnt they would be accessed if the code (spell combination) was given to them.
There would also need to be a global cooldown for each element addition (so players don't cheat and make macro's) and perhaps a mana cost per element type addition to the combo.

This is just my current take on the idea if anyone has anything to add, change, or to just scrap my design all together and come up with a better way of acheiving this or discuss alternatives please post with your ideas and maybe soon this will come to life! :D