If you'd like to use Qabalrin shadow rituals, then using an Umbragen drow is fine, though of course you'll need a reason for him to leave the Ring of Storms. My concern was more that the way you've described the backstory--traveling to Stormreach and Cyre, having his family die, etc.--seems to make the character very detached from actual Umbragen culture. If he's an actual practitioner of rituals, however, that would mitigate it to some extent.
Well, it's not so much actually using those things as having that particular heritage, the Umbragen has shadowstuff in their bloodline, so to speak.
As far as my train of thought goes, an elf with a very strong affinity to shadows/darkness works. Umbragen seems to be the best fit in the lore that I can find without truly starting to dig around for something that may not exist. Although we're talking about Eberron here, being born or conceived in a manifest zone to Mabar while that plane was coterminous, could quite possibly do the same trick, and frankly makes for an easier explanation.
Mostly, I'm just fishing around for a couple of hooks to work with, and then start to work on piecing it together.
If you're looking for an elf with an affinity for shadows/darkness, rather than wanting to explore drow culture, perhaps you should consider a Phiarlan/Thuranni bloodline? They bear the Mark of Shadows, after all; and the dragonmarked houses are a lot easier to tie into Cyre and the rest of the plot then far-off tribes in Xen'drik.
I have kinda formulated the ideas in my head such that the character needs to be a non-standard elf, a dragonmarked elf isn't very different from a non-dragonmarked elf.
In mechanical terms, what I have in mind would be something like taking an elf (or drow) and slapping the dark creature template on it, which would be a lot more removed from your standard elf than just slapping a dragonmark on him. He's different, physiology, outlook on life, that's so ingrained in my mind right now that I probably need to have my backstory start in Xen'drik either way.
JD, @eyes, I have one worry; if Kormác has wolf-eyes, wouldn't it be too obvious that he is a werewolf? It seems to be that the majority of people revile and persecute werewolves on the spot, so it would be really hard for him (or anyone else, really) to blend in, while that's not what's cannon for the lore (the way werewolves used misdirection and subterfuge to send the Silver Flame against the shifters, etc, during the Purge). It seems to me that werewolves shouldn't have any "telling" characteristics while in their humanoid form, else it wouldn't be hard to single them out, and at the same time the rules you linked imply that all werewolves have their senses enhanced even while in humanoid form. So I'd take from this that they don't need to have special wolf-eyes to see in low-light (the Curse is, after all, magical, so why restrict their abilities to normal biology when so many other things are attributed to magic?).
All in all, if you decide that you absolutely require the wolf-eyes characteristic, I'll comply with it, I'm just putting forth some good-natured arguments (though it's not my intention to bother you with them, and neither I am too set on having the low-light vision either, I just love me some healthy discussions ).
@jalapeno_dude: Glad you like it, and thanks for the direction! It really helps to have that kind of outline or set of questions to answer when fleshing out the character. Not to mention the fact that answering said questions has given me a number of interesting new ideas. To that end, I've added another vignette, and an OOC history that will hopefully add some perspective about Sebastian's life.
Just a few notes on some assumptions I made - given the availability of newspaper as detailed in Sharn, I figured that having Sebastian self-publish was a fairly reasonable idea - after all, paper is much cheaper in Eberron, and Amanuensis is a 0-level spell, so having reasonably cheap access to a printing press for-hire seemed a logical idea.
The idea of of the patronage that Sebastian enjoys is built off of my knowledge of the same institution in pre-industrial England - a good example of the concept is evident in the novel Caleb Williams (An excellent read, incidentally.)
I've updated the submission appropriately. Sections with new content are marked with New next to them, for your convenience.