Specialized organization

I'm a volunteer with my local GLBT center, and have been trusted with developing its library of GLBT materials. We have plenty of donations to fill in the provided space, along with procedures in place for acquiring titles, weeding, and circulation. My current issue is that I've been trying to figure out how to organize materials on the shelves. I'm a Library Science student, so I'm familiar with the LOC/DD schemes, but I think they're too extensive for our collection's size. I want to set up something that's easy for visitors to understand and browse.

This is what I have so far; fiction is organized by author, with G, L, B, and T arranged separately (anthologies following novels). That's been well received. But for nonfiction, would it be best to go by subject (homophobia/religion/coming out), or to stick to a numeric system like LOC?

Any advice on this would be greatly appreciated.

You don't need a numeric system. A list of ten to twenty broad topics should do it. When I had a similar project I took a random sample of about 100 books and sorted them by obvious things I thought people might look for (in your case I might pick something like : sex manuals, current politics, history, gender studies, religion, self-help, and technical social science studies -- Hmm, maybe sex manuals could go in self-help). Any book that didn't sort into one of the categories I picked, I set aside. If there were any obvious categories I'd overlooked in the reject pile, I added them. Then I did the "hmm, are these really different?" and "This pile is huge, maybe I should split it into sub-categories". Then I wrote scope notes for every category where it was confusing how to distinguish what went in it. Then I got my pile of left-overs and looked at whether they would fit in an existing category if I tweaked the scope note. If not, the next question is does it really belong in the library? If so, you make up a new category.

Then you type up the list of categories with the scope notes, give it to someone else and give them 100 books to sort. Look at what they did and, when it doesn't match what you'd do, talk to them about why they put it in the category they did. Tweak the scope notes again.

My system has proved fairly robust and lasted a couple of decades through 4 or 5 different people doing the sorting.

PS: There's some literature on this process from the late 1970s-early 80s. It's usually called thesaurus creation. Sometimes it's in books on creating vertical files.

This library is organized by broad topics such as religion,sifi, biographythen arranged alphabeticaly by author ( except bio which are arranged by subject) using sociology as a cath all.. When enough titles accumulate we've organized sperate women's fiction & mysteries. Since we keep this data base we use the organization to locate a title on the shelves after we look up a subject or author for a patron.

I'm cataloging a Gender/Women's Studies Department Reading Room.
A significant benefit of using LOC over Amazon is LC Subject Headings are imported automatically. (Dewey, LCCN and other things, too.) Granted, they're far from perfect and not a replacement for tagging. However, they're great for searches.
Added bonus-avoiding Amazon and its persnickety ISBN override (and general politics.) :)