I would suggest around 10-15 corys. You can have one species, or a mix of species; if the latter, get a minimum of five of each species, so 2-3 species. More of a species is always better. If you intend spawning the rams and rearing the fry in this tank, just be aware that any catfish (corys, pleco, etc) being nocturnal will almost always eat the eggs, or fry should the eggs survive.
Another wood I particularly like is Malaysian Driftwood, a very dark brown solid heavy wood. This is ideal for plecos. Grapewood I would avoid as it has been known to harbour a deadly toxic fungus. I nearly lost fish, in fact once I did, and I have known others who had entire tanks wiped out in days.
One comment on the suggested stocking, relating to temperature. The common or blue ram needs warmth, around 80-82 F. Neons will not last long at this high a temperature. Many corys the same. Cardinal tetra would be better than neons here.
For an Amazon biotope you could go with plants and have more of a flooded forest aquascape, or go with a stream/creek aquascape with no lower plants (just floating) but lots of wood and branches, and dried leaves over sand.
Byron.