I would be worried about keeping Harlequin Rasboras with the Severum. Once it gets big enough, it could start picking them off.
I personally would go with the Severum, the Denison Barbs, a school of Columbian Tetra, and maybe a school of cories if you want (or a BN pleco).
I personally would go with the Severum, the Denison Barbs, a school of Columbian Tetra, and maybe a school of cories if you want (or a BN pleco).