In one level, this system encourages you to purchase 3 ranks in 5 lists.
However, the "lists worked on" an change each level
Thus
L0 = no lists developed (focusing on other skills - the character's childhood/adolescence; would recommend things like hits, combat, climbing/swimming/riding/perception)
L1 = 5 base lists @ 3rd
L2 = 10 base lists @ 3rd
L3 = 5 base lists @ 6th, 5 base lists @ 3rd
etc ...
from then on, a pure spell user always has c. 10 lists "to level" and either a good number above level (for over casting or directed spell development ... for example, until you have firelaw to 6th level, you cannot start to develop the "fire bolt" attack skill )
A semi spell user will not be able to afford such a dev cycle, but should be able to maintain 3 or 4 lists "to level"
developing more than 5 lists per level is inadvisable ...