Just to tell you how the insignias work in Szith's Sorciere...they're based on your base class: only wizard and sorceror levels count.
First tier: Able to cast 3rd level spells (5th wizard. I assume it's coded for 5th sorceror as well even though they get these spells at 6th)
Second tier: Able to cast 6th level spells (11th wizard. 11th sorceror as well I assume, doubt it was coded for 12th)
Third tier: Able to cast 9th level spells (17th wizard, possibly coded for 18th sorceror)
So in Szith, I think reaching 17th wizard makes you a master, and you may also wish to play that e.g. 7th wizard with 10 arcane scholar is also a master.
It's pretty fun to play the apprentice and advancing in rank stuff out in-game of course, but those who don't have someone handy to guide them sort of assume it's happened "behind the scenes".
Of course I'm more than happy to give anyone "guidance" with Istinid, so have your characters give him a ring : )
Just bear in mind that while I know tons about the game mechanics of NWN2, I'm a bit of a neophyte when it comes to the lore behind the magic in FR.
This might be a good starting point: http://forgottenrealms.wikia.com/wiki/Magic
, but I'm not quite sure where to go from there.