I had done this with one character. I had also developed the spells with circles to make it more efficient. At 12 pawns or so I found it expensive enough that people didn't jump on it so quickly. At 4 pawns or so, everyone wanted as much as possible. With half a dozen in a circle, you get a nice profit. I also had Good Teacher and made sure to boost my Communication as well as Intelligence.
That earned me a lot more. I had specialized in CrMe and in Magic Theory. I had built up my Magic Theory so high compared to everything else it was scary. I also trained up Teaching. 3+5(Com)+5(Good Teacher)+6(Teaching)+1(specialty)=20. Now imagine a single season of teaching two dozen magi. I allowed multiple payment methods amounting to an average of about 2.5 v.f. per person. (Some of it was in silver so I could afford to feed them.) Would you pay 2.5 v.f for a season working with a quality 20 source? I expect so. Now multiply that by 24.
Stats improvement is one area of magic that's desperately calling out for additional limitation, IMO.
It's barely tolerable when a magus does it to himself. When it comes on the market via this sort of specialist it gets way out of hand. Imagine all the magi with +5 everything and all the cool books they can write.
One option I'd seriously consider is making the magic warp everyone as an ongoing effect, regardless of whether the spell is expressly designed for them. Magical intelligence sounds pretty unnatural to me.
To make Jahir's uneasiness with the rules more profound let me just point out that your ritual can be range touch duration instantaneous and target circle for a final spell with a level only one magnitude above the guideline. Of course as always, that 's just a guideline not a rule.