If you add too many neons, they may not feel the need to school. Additionally, though a school of 8 is entirely sufficient numbers for the cories, I think they'll look much more impressive in a bigger group. I'd go with 50 neons, and 25 cories.
actually a fishing show on VS. right now (hunt for big fish with larry D), guys down fishing on the amazon and pulling out soem really nice P. Bass and some stuff i don't recognize. he was jsut doing some fishing in a blackwater pool and pulled out sometihng i didn't recognize but was really big and aggressive, maybe a wolf fish.
anyway, as far as true blackwater habitat goes, its pretty sparse for plants most of the time. plants in the wild tend to be spread out more and not nearly as nice looking as most aquarium keepers keep them. also tends to be a lot of algea. the reason you don't see a lot of mention of rocks in blackwater is because the pools tend to be pretty still most of the year with a dense layer of organic material thats not yet decomposed and algea. without a current to move rocks, they tend to have silt bottoms under the organics, i've read that in some pools this can be a foot or more deep of dense matted leaves at the bottom. the pools are usually pretty heavily shaded by the trees growing over in the true rainforest. once you get into the creeks where you have a little more water movement, you'll have less of the organic bottom, but still may have black water.
With a low PH the bacteria that breaks down the ammonia/nitrite/nitrate cycle is not very good, so the BIO load must be lower too. I would only go for about 50-70 neons plus cats.
I've decided to go with setup http://fish.mongabay.com/biotope_rio_sucasari.htm .
I went looking for wood but didn't find any that was branched like I wanted so I've got some dried Sparkle Berry that I've sandblasted clean. I'm not sure how long that it will last in the tank so I'll need to keep a close eye on it. I'll post a couple pictures tonight when I get home of the wood and the current tank. For the added filter what do y'all think. I would like a make that I don't already have. I have Marineland, Rena.