You'll get so much more out of your tetras and cories if you bumped up to a 29 gallon tank. Go for about a dozen serpaes and 5 cories (Pandas are nice, Sterbas too, I find that Aeneus cories are a little less shy). Toss in 3 otos or an albino Bristlenose, plant with Amazon swords, and tuck some driftwood in there if you have a Bristlenose and a couple of caves for the cories.
If you have to stick with the 10, you'd be better off skipping the cories entirely and putting in about 4 kuhli loaches. Pygmy cories (and the similarly sized C. habrosus and C. hastatus) really do best in schools o 10 or more.