Since I heavily used RQIII sorcery, Sandy'e sorcery and MRQ sorcery, I can answer the question.
-RQIII sorcery
each spell is a skill (raised with a skill check),
each manipulation is a skill (raised only with training or research),
the spell's manipulation is limited by the Free INT (but if a spell matrix is used,any manipulation enchanted into it is added)
There is no limit on the number of spells the wizard can have active at a given time.
The trick is to remember that a spell with duration 10 lasts 1 week, and duration 16 means 1 year (64 weeks).
So with careful planning a sorcerer can have his defensive spells up for a long time, and have enough magic points to be useful to his comrades.
Let us remember the stupefy spell (pagans have low free INT), or the drain spell (fatigue points are removed) that can be cast at more than 500 m (range 6 = 640 m), and that can be really nasty, if a sorcerer wants a direct attack spell.
But, it is true that the bookkeping is heavy.
Begining characters are weak, but even experienced ones have always something to do to be even more powerful.
-Sandy'sorcery
each spell is a skill (raisable by experience)
each manipulation can be a skill, but usually is an art (either you have it or not)
each sorcerer has a presence.
the spell's manipulation is limited by the free presence and the skill in the spell
the number of spells active at the same time is limited by the presence.
The bookkeeping is lighter than with RQIII sorcery, but it's manageable.
My worst nighmare is someone with a spear affected by damage boosting and Wachaza's Fang ...
-MRQ sorcery
each spell is a skill
each manipulation is a skill
The outcome of a spell casting is more complex to know than in the previous versions, because the manipulation used are determined by the result of the dice roll.
(ie a sorcerer can succeeds in some manipulation and fail in others)
It is much less costly than the previous version, but the linear scale used for the range and the duration manipulation means that begining characters are even weaker than before.
A befudle spell has a range of POW x 10 m, and only a sorcerer with a range skill of 91+% can hope to equal this.
And as RosenMcStern wrote many spells need to be rewritten.
Cheers
Jean