Hehe, I admit I had to take a bit of a breather before I tackle this one, forgive me for taking a while to respond!

For starters, well I admit I can't argue with an old family story!
I'm not sure, but I kinda get the impression by your reaction to the hats that you might think I've overstated something. 'tis fair if as you've said, most resources you've found understated it, which is a claim I can indeed support, but that's because of 2 factors: The alp is still obscure outside its country of origin and most resources have picked up from where others left off, omitting things from time to time as they do. On the internet, like I mentioned, most info on the alp is taken almost verbatim from Matt Bunson's Vampire Encylopedia. However, his 3 paragraph description is often abridged to only describe the alp as a German vampire-like entity, and leaves out both the hat and the evil eye. So it may be true that not many sources mention the hat or its importance, but being often omitted in favor of succinctness does not mean it's not a part of the mythos. Most often a resource will say what the alp does, and leave it at that, with little to no description of how the alp appears.
Many sources that did not originate from Bunson's entry may only describe the alp as a white butterfly that comes out of a witch's (or a murrae's, or a human who is being cursed) eyebrows, and I'm fairly certain from your description that this is not the alp that you're familiar with. The white butterfly mixes together with the alp's description in nearly all accounts that describe it wearing a hat, however.
If it does not mention it's shape-shifting abilities, chances are they don't mention the hat, either. Again, being omitted does not necessarily mean it's not part of it.

Mares and Maras are often times beautiful but malevolent women (but more often hags) that victimize sleeping people in a similar manner to the alp, but that is not necessarily the alp's origin. Alps are descended from elves/dwarves that lived in the mountains, and many key elements of the alp are derived from the story of Albrich, a dwarf king who had a magic 'tarnhelm". As far as the alp itself goes, alps were once friendly beings but slowly became evil and mischievous when they left the mountains.
Alp alternately can mean "elf" or "shining white one" (in reference to the white butterfly no doubt, or the white mist it becomes. Others contend it is the alp's complexion)
The alp's tarnkappe, and even its name (as sometimes it is called an "alb") are said to be remnants of this legend of Sigfried and Albriech the dwarf. Eventually the alp coalesced with the legends of maras and similar beings (truds, doggis,walrider schrat, and the habergeis which is a demonic bird/owl which gives us the alp's ability to fly) and formed what we know today as the "alp." The alp as we know it today in fact is widely regarded as a goblin, demon or an evil spirit rather than by its elfin roots.

Similar beings, like the shrattl/shratteli are like the alp but sound a little closer to your description. The shrattl particularly enjoys driving people insane with its nightmares, is a far more malevolent creature itself, taking great pleasure in tormenting livestock and people.

Where the alp gets it's "vampire" connection is the tendency to either taste blood from nipples or to enter the body as mist and absorb it that way. However this is not common as it's modus vivendi is to "ride" and cause nightmares.

Please don't take this the wrong way, but if you did not like certain elements of the alp, why not make an original species? In my experience, people are apt to praise you for the originality instead of gripe about the accuracy of the mythology ^_^
He sounds like an interesting character but I think that by the very virtue of not drawing him as either an elf-like or goblin-like creature (or in some cases, a hairy little old man, for example [link] was someone's interpretation drawn before this club account went up) it's already significantly different from the alp mythology most of us are familiar with, the lack of the hat just further distances it. And I suppose I have difficulty understanding why you'd choose the alp considering how you do not like the black magic elements, because you'd have to do away with a lot more established mythos than the tarnkappe since black magic permeates the alp's very existence, from its tendency to be a summon to its "evil eye" (I suspect this is not a part of your OC as well, but I may be wrong!)

That's not to say that you don't have the right to do as you see fit with your own character, or that it is unfair to mold something in your own creative vision, but typically when people "modernize" a subject it is one that is well known and established, cliche and tired, and they're adding a new "spin" on it. If you're picking a creature that's already obscure and making drastic changes to it, you might as well make up something new since it defeats the purpose of being contrary to the built up expectations one might have established in regards to the mythology. Like for example, a zebra unicorn, or a gryphon that is part owl/part leopard instead of a eagle-lion.
These deconstruct expectations while keeping a semblance of familiarity that people use a reference, because they are well-known creatures.

Please please do not take this as me being catty or a know-it-all,(hehe 'cuz I don't!) but I have a rather large following of German readers for my comic that have helped correct my improper grammar whenever my alp character speaks in Deutsche, I don't think they'd be afraid to tell me I'm bungling the character's mythology (in fact they've been tremendously helpful finding information for me!)and they have often supported much of how I represented the creature for the past 5 years I've had my comic online. This doesn't give me the authority to tell others what to do however, I'm just saying that many people that have expectations of the creature may have only been aware of it thanks to my comic, which until only recently was the only webcomic with an Alp character in it, and this is why I made sure I did my best and most thorough research on the creature before committing it to paper. I'm not completely innocent of a little reinterpretation myself, but for the most part I've remained loyal to the mythology.
However this club was not started to have a bunch of people draw the alp exactly as I see it, but to take a look at the information and form their own vision of it. I made sure to encourage people not to draw alps like i do, but how they think they might look! I may like how I represent the creature, but I've seen some fantastic designs come from this club as well that sometime I wish I'd thought of.
That alp is one confusing creature to nail down though!
Please don't be upset by this text wall, I just wanted to explain things the best I can ^_^
I'm not gonna try and encourage you to make changes to your character, clearly you are attached to him the way he is, and I apologize if any of this has upset you in any way, it was never my intention to do so!
If you'd like some links to some resources I'd be happy to oblige as well ^_^

~Amy