Re: Spells
Could there not just be a generic "magic-user" talent as a placeholder for however magic is defined in a given setting? Establish that a character has talent with magic, and then go from there.
Since I personally prefer the skill-based method that is described in the core rulebook, but would still want my players to take a talent to start things off, why not make it a d6 talent--this can unlock the ability to take a skill related to the kind of magic they practice, and then can specialize accordingly. On the other hand, some people will prefer to keep magic talent only, and use the spells as complex, rather than simple actions as if magic was skill-based.
Regardless of which method you want to use to represent magic, there should still be a "default" that then can be further defined in-universe to reflect how magic is handled in the setting.
As far as spells are concerned, perhaps the # of spells that the character knows, or has access to in a given day, can be defined by the level of the trait or skill/specialty that defines the character's method of spellcasting. Granted, this will be heavily influenced by setting flavor, but again there should be some sort of default (spells per day, get a new spell when your trait or skill increases, cast x number of spells spontaneously from a given list equal to your trait or skill value...something).
My two cents, for what it's worth.