I just stocked a tank with 20 young demasonies. If you want a challenge, do dems, they are one of the most aggressive and are high on the price scale. Although I got mine for 3 dollars each because I got an employee discount on the order. But we sell them for 20$ each adult. THEY ARE MEAN!
Also the venustus is one of my all-time favs, I like the juveniles because they don't have the blue face yet and I like that better. Just know, they get massive. Really big!! Good luck finding a stock and you have a good looking set up, well done! I enjoy a species tank as much as a variety tank. Happy fish keeping!