just have one realm of magic: essence. All list are essence list. Base list train at 8/8/8, closed at 6/6/6 and open at 4/4/4 for ALL professions. If you wish, a PC has to buy a talent that allows them to cast magic, as in GURPS. You could even stage the talent (able to learn Training Package list at 2/2/2, Open List at 4/4/4, etc, say 5 talent points, 10 tp, 20 tp and 30 tp respectively).
That is the easiest way. Additionally, PC's have to find their magic spell books to study, or buy them, etc.