In a word, no, I'm afraid not
The tank is very heavily stocked as it is. The Knife fish should get to 18 inches +, and the angels will be small dinner plate size once they finish growing.
These should be re-homed before you get too attached to them. Once you are attached, letting go will be harder, even though keeping them would be unfair for the fish. I know, I've been there
The red shark will need a minimum of 50gal also once fully grown.
Looks like a typical case of poor advise from your LFS
If you can re-home those above, some small bottom dwelling cats would be do-able, say a group of 6 pgmy corries
Plecos will get between 12 and 18 inches, so are best left at the shop. Bristle noses are a consideration for the future, but they are heavy waste producers, so would not be suited to such a heavily stocked tank just yet. In a few years, once you have lost a few fish, one might be possible.
IMO, the space the re-homed fish would provide, would be better offused to get the groups of the other fish up to their recomended minimum group sizes. The Tiger Barbs realy need a group of 6+ If the plattys are a pair, another Female should be added, to reduce the stress on the single female, from the male constantly wanting to breed with her
All the best
Rabbut