So, I've got a player who's statting up a sponsored magic user... I want to confirm my understanding...
The character does NOT have any unsponsored magics. It's all from the source.
Sponsored magic and regular magic work pretty much the same way, the main difference is in justifying why the character has magic, as well as a few additional benefits from the sponsor.
Evocation
The character decides how much power to call. Does he still take one mental stress for calling the power?
Does conviction still act as a limiter to the amount of power that can be called (before taking mental stress?) I'm assuming no, since he's not taking mental stress for calling the power from another power-source.
If these gloves are off, could a guy potentially choose to call 10-shifts of power, so long as the sponsor okays it?
He takes casting stress like any other magic user. 1 shift for each spell +1 shift for each shift of power above his conviction. Sponsored magic does not absolve you from this.
However, the character can ask his sponsor to absorb the stress for him, in exchange for increasing the debt towards the sponsor.
I presume that Discipline is still needed to control the power, though. Right?
Yes, it is. Again, you can ask your sponsor to help you, if you fail, or if you want to get more oomph out of a spell. Usually the exchange rate is +2 per point of sponsor debt, just like invoking an aspect (because that's effectively what you do).
Thaumaturgy
Given that this is at evocation-speeds, the sponsored caster doesn't have to waste any time.
Does his Lore rank make any difference to the actual casting?
Does Conviction matter in sponsored thaumaturgy?
Thaumaturgy at evocations speed and methods basically means, that your evocations become more versatile. You can, for example, cast skill replacement spells, which evocation usually can't, in the blink of an eye, that would usually take you at least a few minutes.
You determine the power and the casting stress with your conviction, and you draw up the power in one discipline roll, just like it were a regular evocation.
Lore is still used in sponsored thaumaturgy, if you want or need to cast a spell that's too complicated to do it in one roll. In that case, it is no longer "thaumaturgy at evocations speed and methods", but regular old thaumaturgy, lore determines the base complexity and everything. Your conviction matters here as much as it does in regular thaumaturgy, as it is the number of shifts of power per exchange you can safely gather, without taking casting stress.
I"m super-tired and not focusing, so I might just be missing all sorts of stuff. I'd hate to tell this guy how to do things then recant later.
Hope this helps. Sleep is god, go worship.