Pepper cories usually aren't found in blackwater, as I understand it. Clear flowing water is more common.
Serpae are often found in blackwater, I think.
A blackwater stream tank is fairly simple as biotopes go. Go with a sand substrate, a few chunks of fresh malaysian driftwood(to release lots of tannins), and some floating plants. Light doesn't penetrate down into the water, so you want floating plants not rooted plants - Salvinia and frogbit are good choices.