Fine calculations all - but one fatal flaw in the OP that should be faced. The whole of Tamriel is bathed is magica - so there is not 'without magic' because magica is an intrinsic part of Tamriellian existance.
True certain individuals are demonstrably able to harness it openly and others do not appear to do so - but who is to say that those non-magica-users do not use it unconsciously? That may well be part of what sustains the Gods for example.
I hadn't forgotten that, of course. I realize it's everywhere - kinda like the force. I think it's the ability to harness it which counts as having it "inside you", though. It sort of floats around the atmosphere, flowing through everyone, but those who master its use build up a large resevoir inside themselves, which is at their disposal. It probably has a sort of restorative effect, constantly rejuvenating the person's body and mind.
re necromancy - we are still learning what that is about. What we mostly read about is the 'icky' side of it. But folks believe that is only one side of it and there are Necromantic studies and practices that are not connected with raising skellys and jelly-blobs so perhaps Restoration is in part Necromantic?
I believe the Necromancy the Telvanni practiced isn't exactly akin to that of Mannimarco and his lackeys. I do believe the term could be extended to cover almost any power over life and death. The Telvanni Lords are a bit creepy and isolationist, though, and do keep many slaves. I imagine dark rituals behind closed doors in which a young, healthy Khajiit slave is drained of his life force. Deep wrinkles appear in his skin while they simultaneously disappear from the Telvanni. I think that would be a sadistic but interesting aspect of their Necromancy if it were true. I got the idea from http://www.youtube.com/watch?v=BPaKNafdJ18.