The shark is not going to be happy for very long in that tank. In my experience with tiger barbs if they are introduced into a tank after less aggressive fish are established, they don't chase them as bad. If they are established in a tank they chase about everything you add. With only three of them they will likely nip at everything else anyway. I try to keep groups of 6-8 so they play among themselves. I never really considered tiger barbs that aggressive. I have a 29 with 5 tiger barbs and 4 green tiger barbs that all school together, 3 black skirt tetras, and 1 opaline gourami and they seem to be getting along fine.
My 29g Project.
No, an oscar will not be a good tank mate for barbs unless the barbs are there for food. He will get big enough to eat them.
If you are looking for aggressive why not give the New World Cichlids a look? Some of them might do well in a 29g tank and from what I have been researching are rather simple to care for.
Take a look at
Aquarium Fish: Tropical Freshwater Fish and Saltwater Fish for Home Aquariums and you will find several of them that are suitable for 30g tanks.
Please note: I have not kept any of these cichlids, I only mention this because I am researching some types for a future 55g setup that I will be doing and it seems to fit what you are trying to do.