hey there guys, i rencently inhereted a 50 gallon tank, and want to run a showpiece tank, i currently have it empty, but is cycled, i will be putting a 6 inch female Jack dempsey in, along with a 4 inch red tailed shark, i was thinking something a little bit more agressive by maybe introducing two 2/12 inch, or 3 inch red bellied pirhanas. as well as a black ghost knife fish, this diversity in the tank is what i want, but i really want to run sand as a substrate, i also have a group of cons, one male 6 inches to 3 females about 4 inches, would a pair of these work as well?

as for stocking properly, i realize these fish arent idealy kept with the ones ive mentioned, but if it would work that would be aweosme
i also wouldnt mind a German blue ram

any input would be great!