This is a very interesting concept, and such a character makes a lot of sense in canonical Theban Tribunal, with some small changes if we are in a canonical Theban Tribunal. If so, potential apprentices are presented at Tribunal, and then are given out to worthy masters. Your character could have found some interest in candidates not typically found in the usual means, and probably has garnered several tokens by finding apprentices over the years and presenting them.
I'm not sure what legality you're asking about. There are mundane laws that need to be considered, sure. In light of that insert, I'm sure those slaves are purchased, probably at a premium by Coeris, over other comparable slaves. It's silver, who cares. The real legalities come when you try and entice a Gifted child away from his parents. Is this bringing danger to the Order through his actions? I seem to recall mention of magi kidnapping their apprentices, but I would think that's a rare apprentice and/or a powerless and penniless family that can't do anything about it.
I'm skipping the a) question, as that is addressed more towards a specific player.
Here's one that has it as level 15 Nestor ex Misc.
I have a bit of a problem with that, as Base 10 is detecting Magic, either Weak and recent or powerful. Is the Gift magical? I tend to think it is not. I think you could perhaps detect that such a child worked magic recently, and that's about it. Thinking about it another way, if there were a simple spell to detect the Gift, House Jerbiton would've long ago invented it, if only to find those Gently Gifted souls who never get discovered because they blend into society and don't get noticed.
This goes hand in hand with the interview period describedin The Sundered Eagle, but to a magical degree. Unfortunately there is no guideline that currently exists. Perhaps no one has thought of it it, and it is some original research your character needs to accomplish? A Trianomae conducting original research would be a hoot, scandalous and something to be expected of one with a Tytali heritage. I can see the comment now, "Well why can't I conduct research?!"
Sure, but I think you have an excellent in character reason for wanting to know the capability of the apprentices you present to the Tribunal AND you can use that as an edge and turn the apprentice process on its head by controlling the flow of information about the apprentices you have discovered to the individuals you wish.