I suppose I am more or less qualified to answer you. My 28 gallon community tank has a somewhat similar composition to what you seek, though perhaps less crowded.
You can get all male dwarf gourami, and might have a difficult time getting any females if you wanted them, depending on the fish stores at your disposal. I personally have never seen a female gourami, and I live in a heavily populated area. Because the females are rather plain, stores tend to carry only the colorful males.
I have four dwarf gourami in my tank and they are not only fine with each other, they are fine with everybody else. They are a joy to have in my tank.
I am not familiar with diamond tetras. I have black skirt tetras. They chase one another around the tank when no one is looking, but they play nice with others. I love watching them eat -- like little pirhanas. Some tetras can be nippy, I guess, but I think if you have several they are ok.
Cories are the best. My bronze cories are too skittish, though. Some people will say it is because I only have two, but I had three plus a pair of peppers, and the bronze were psycho then, too. My peppered cories have been the most hardy, good natured, laid back, and lovable of fish.
I don't know about algae eaters, except that many get way too big for my tank. Do your research on those. I don't seem to have a problem with algae, I just use an algae cleaner every once in a while when I do a water change.
Unless your water is absolutely ideal for neon tetras, you may have a rough time keeping them alive. Most people seem to. It's the breeding practices, I gather -- they are just not healthy fish. Best of luck with that. Otherwise, your tank sounds like a winner! Happy fishkeeping!