First off, welcome to the community! It's refreshing to hear that you've already done some research into best practices (for this forum, at least), which already puts you leagues ahead of other would-be collaborators.
That said, there's still a difficult road ahead I think. The two points you've identified as potentially problematic are spot on I think. The first one, anonymity (for now) is definitely the easier one to fix 
If you pick out a profile picture and hang around for a while and participate in some discussions, I'm sure people will come to know and recognize you 
The second point is the killer for most collaborations presented on this forum, BUT that you've already identified that it is potentially problematic is great and means that you can try to find a way to work around it~ The reason that long projects are typically shirked when they're pitched for collaborations is because they just take so, so long to draw that it's often not feasible for an artist to commit to finishing. People work at difference paces and the level of quality and rendering style does impact that, but like looking at the "greater than 1 year benchmark" in the OP, for me that's about how long it took me to finish my first one-shot of 70 pages here on Tapas. 14 months of consistent work, with a few months of less consistent pre-production before that. So that's, like, 3x longer than a shorter like 20 page one shot, but still only the equivalent of a single story arc or about 3 chapters.
Being a paid collab will put the project a notch above any unpaid collab, but the problem is- unless it's paying exceptionally well (like enough to replace my day job) or unless it can be completed in a reasonable amount of time, it's still not going to look very appealing because I don't want to be left with an unfinished project on my resume that took months of my life for a small amount of pay and isn't even my story. Even if it were enough to replace my day job (and thus allow me to work on it much faster, the above benchmark was considering that I was working full time the entire 14 months), it's still going to be a risky proposition because, frankly, unless you're independently wealthy it's not a particularly secure job position. That's a lot of money out of pocket to pay for a product that's likely not going to turn a profit in return.
Doom and gloom aside though, this doesn't really answer the question proposed- which is what's the best way to take a stab at this? I pretty much second what ar-ninetysix said above about first and foremost starting out by producing some finished quality writing. Whether you want to post literature here to tapas or just keep them in your back pocket in an online portfolio to share with potential would-be collaborators, having finished works to show off will immediately increase your credibility. This goes hand in hand with ingraining yourself in the community. If we know who you are but also that you can write quality stories, that makes working with you much more appealing!
Further, aim to produce some finished products at specifically the length of story you would like your comic to be. Granted writing prose and writing comic strips are different (though, related) skill sets but I think it's important to see for yourself what you're working towards, and that will give the artist a good idea as well. Not to say that the "practice' stories necessarily have to be the story you want adapted- that's up to you. Maybe it would be easier to sell someone on adapting a story that they can see exactly how long it is and what it's about, but maybe for a collaboration you would rather develop that story in conjunction with your partner and instead would rather write unrelated examples? Dunno.
This wound up pretty rambly but hopefully there was something of use buried within xD I guess I'll slap down a tl;dr to conclue:
tl;dr
Re: the above reply. Start by developing yourself as a writer and then you can begin pitching your ideas. Just be aware that a long-form collab will be difficult to find, even paid.
