MI3 like lilnaugrim said I would also take the cichlids out, because they are aggressive fish.
I have my whiptail I'm a 20 long, I don't care for hight on tanks to go more for the floor space. Because I know when you hear 6inches you think big fish, well no, they are skinny fish that take up no room, yes 50g is an ideal size, but if you do your research you will also read they like strong currents, that would be a PRICY filter with out a dought lol, also I read a lot of posts that said they have success in "long" 20gs +. So I put a nice currented filter, and have a lot of plants in my tank( they need and love to have a heavily planted tank) they also like wood in there tanks.
I live at a zoo lol