For an ArchMage type of Character...... Hmmm.....
As for Arcane Magic (being treated as the root of all magic), I would consider that to be the Spell Bases, from Libram Novus #1. Just follow the rules for learning and using Spell Base
Now, if you want to treat Arcane Magic as a seperate Realm, you would need to actual create that Realm and decide what spells are wanted as part of it.
And for an ArchMage, I think I would likely do something similar to the Harn Wheel of Magic. There are 8 core Schools, And the Universal Spells could act like Grey spells in Harn (basically the same, learnable by all).
Attached is an image I just made up.
A Circle Divided into the 8 Schools of Magic (the underlined words). Casters are listed (same size as the School Name, but not underlined). Mixed Classes/Training Paths listed in smaller size. And those with quasi-magical abilities are list in parenthesis ().
Dual Mage would be allowed any 2 (though, looking at this, I might limit to those not directly opposed), and an Archmage could be one who learns all but the one opposite (One Primary uses Major costs, the two directly beside the Primary uses Minor costs, and then the next 2 use Non costs, leaving 3 Schools unaccessible (which allows for a good bit of variation).