This is for a fledgeling bad guy right?
I surer hope so because the wardens would be all over this guy.
As for the rotes:
I'm almost certain that the greater version isn't totally in line with the rules. So this guy is using his stuff on his fellow class mates right? To inflict a mild consequence you have to do an outright attack ritual. It's save to say that the pupils wouldn't have a conviction above 3, if you wan't to be sure to inflict a mild consequence you'd have to invest at least 11 shifts of power (3 for approximated skill level + 4 to cover the possible defense roll + 4 to deplete the stress track).
Now the other part of the spell is a maneuver on the caster himself. He won't defend against it, so the base difficulty is 3/good. To make it sticky there is an extra shift needed, witch makes the difficulty 4. Depending on the desired duration of the effect the complexity would have to go up +1 with every step on the time table (starting from 15 minutes as this is the average length of a scene). So far so good. The complexity of everything combined so far seems to be 15 shifts.
As a GM I would add an other +2 requirement on top of the spell to reflect the difficulty of combining the two effects you desire. That brings the complexity to at lest 17. The "Stolen Intellect" aspect holds for as long as you have designed in the construct of the spell and not only for two invokes (the first tag of cause is free). More shifts don't give you more uses. They just prolong the effect of the thaumaturgic spell.
17 Shifts isn't something you do easily. I doubt it could be done as a spur of the moment ritual in some shady high school restroom. Come to think of it. Even 14 shifts isn't something a newbe warlock could pull of easily without tapping into a lot of stuff.