how will you distinguish this from Magicka, which uses a similar system?

This implies both that I want and have to.

There's a logic behind every combination of elements. Sonic Lance, for example, is produced by combining Sancta - an element of sturdiness and solidity - with Forza - and element of force, energy and movement; so you might think of it as kinetic energy encapsulated into the shape of a lance. Iron Skin is a fortification made of two Sanctas; a shield, when added, would probably consist of three Sanctas or two Sanctas and Forza. So on.

Combinations of buffs and debuffs are to be added with the increase of available element slots. Bleeding, for example, wouldn't work well with poisoning because blood escapes the enemy before the poison has a chance to affect the body. Undead and those without bodies are to be immune to poisoning and bleeding. Thick Air I particularly expect to buff in combination with whatever the triple-Forza spell will be available, so emulate how dense environments transmit kinetic blasts (the energy travels through a medium the easier - i.e., with less loss - the denser it is). So on.

I also thought of adding modifiers to be applied beyond the spell's structure. I expect the maximum spell capacity to be four elements per spell, and any element you might add over that will only increase the effects. It's a hypothetical construct I have to think about still.

Ideas on any of the matters, listed, mentioned or otherwise, are always welcome.