mmmhhhmmmmm, this is just my opinion but personally i would not put roseline sharks in a 55g, mainly because these guys are super active, i think they belong in a 90g minimum, i have personally seen roseline sharks in a 55g and it just did not look right, always bumping into the glass when ever they get scared
i dont exactly know what you want to do with this tank, what i would do is:
10 tiger/green barbs
dwarf pleco of your choice
10 cories of your choice
and some solo fish that would be able to co exist with tiger barbs
or go cichlids, my 55g is over stocked since i had to take in two blood parrots from a friend that impulsed bought them and bought them for his 20g long, but i plan to keep them, blood parrots are really cool fish ^_^