From my experience, an intellego specialist is always sorely lacking and needed.
A longevity magus might be useless if the saga is short, and is more restricted otherwise. I'd advise you to avoid it.
Item creator, well, this does not speak "magus type" for me: Verditi have specialties.
Super Teacher, I'd say no. You're not here to help us maximize our characters (although this is a valid companion concept, OTOH, but for a magus...)
Monster Slayer/Hoplite: Why not, but then, We may have beranger, and this can come easily to Amul and I.
Spy: Interesting, can be combined with Intellego specialist, but beware the code!!!
Trader: Valid for a companion, but a magus?
Say you what? I'd say try out a Tremere, with the Virtue by YR7 instead of the magical focus (unless you want the focus). This may be pretty fine and interesting. And I see chicoazian has similar ideas 
Agreed.
I suggested upping the excellent threads you had done for Characters short resume and Covenants, but that's impossible at the moment.
Also very important IMHO, are 2 threads:
- Submitted spells, for discussion of player-created spells
- Approved spells, for those spells that passed the test of the first thread.