my favorite subject, stocking a south american tank....

i have some dwarf acaras.. great fish... only about the size of a ram too
cardinals would be a great addition... pencilfish would look nice too, Nannostomus mortenthaleri are amazingly colored, or the more expensive, Nannostomus espei
cories in my opinion are a must have, help with cleaning up left over food off the bottom, corydoras sterbai, are my personal favorite however there are tons of different types of cories
hatchet fish are cool characins that stay at the top, just under the water surface, carnegiella strigata, are cool
lemon, bleeding heart, cardinal, etc. tetras would go nicely
just watch out for fish that may eat the rummies or cardinals like angelfish..