I don't know alot about red finned sharks - I *think* they're the same as red tailed black sharks (RTBS) and they're known for being pretty aggressive, so you want reasonably robust fish (unless I'm talking rubbish about the shark.)
Some rainbow fish - Boesemani's look good, or praecox - good dither fish. A smallish plec, on first glance they're ugly but they're easy to fall for. I've got an L15 but theres plenty of others that don't get too big.
Hmmm. Might get away with some flavour of ram, either German Blue or Bolivian - good looking fish. And possibly a single angel as a centrepiece.
**disclaimer**
The only fish of the above I've kept myself are German Blue Rams, praecox rainbows and an L15 - the other suggestions are based on anecdotal evidence, not experience. I'm sure someone will post though who has kept some of the above or can give you some alternative suggestions.
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