I'm not an expert in the subject, but I think that most of this is going to be one part story-flavour and one part declarations.
As you noted, Harry does not have a "Bob the Skull" aspect. Instead, as Harry works on his spells (i.e. Thaumaturgy, Potions, etc), he spends the extra time/effort to appease Bob (so to speak), gets to make a declaration, and viola. This case is explained a bit on YS269. It is also referenced again when discussing the creation of potions, how Bob almost acts as an NPC that causes a compel to Harry's "Perpetually Broke" Aspect (YS281). In both cases, Bob is a resource used without actually being listed on the sheet, whether he is in the guise of a supporting NPC or even just a declaration.
As you can see, this is more of a sample of storytelling than hard and fast rules. I think the designers put it that way for that very reason: this is more of a storytelling game where the mechanics take a back seat.
Now, for your situations, I can see these things as being simply be written off under the respective stories of the characters and have no real intrinsic benefit aside from adding an extra detail to that character. If you wanted them to be used, limit them to how they would be if they were real people.
In the case of your Monster Hunter, yes, he can have students that can cover the shop, so to speak, but I wouldn't expect them to go charging into battle with him without some major roleplaying to get them involved. I can also see these NPCs being useful as Declarations for Contacts/Investigation rolls.
As for the Wizard, I can really see that as a valid option (and leads me to some interesting ideas). I can see it as I have previously mentioned: it's a part of the character's story, and may lead to more of a story in the future. I won't start tossing story ideas out there, but oftentimes deals like this can open more doors than expected.
But in the end, as noted in the books: it's your story, your game, and your decision (even as a player, parts of that seem to stand). That is just my take on it.
Does that help at all?
Either way, good luck and happy gaming!
--Crion