1). Bethesda called me, they said "you're welcome".
2). What does "all the way through" mean, though? Are you talking about all quests, every quest in the entire game? If so, then I've never played Oblivion. If you're talking about the Main Quest / Mehrunes Dagon crushed, etc., then my answer would be once, in 2011, with my Grey Wizard character.
If you're talking about how many playthroughs you consider as "valid" (characters which last until you feel a bond with them), then my answer would be right around ... well dang I'd have to count 'em. Hmm... let's see.
1). Renee Gade (original)
2). Renee Gade II
3). Igodah Go^Pe
4). Wanda Bone
5). Luci Pheria
6). Dyan phor a'Cauz
7). Eradi~Kate
8). The Grey Wizard
9). Kahreem of Weet
10). Lady Saga (PS3)
11). Lady Saga (Xbox)
12). Ann Thraxx
13). Snaat Rayag
14). Lady Saga (PC)
15). Renee Gade III (daughter of RG2)
16). Sarah Phimm
Fourteen. I mean 16.