On the Rainbow Shark,
Epalzeorhynchos frenatus, ...[from the profile I wrote elsewhere] Territorial and combative with its own species; best kept in solitude (as they seem to live in their habitat). Young fish tend to be secretive, but as they mature some can become aggressive, especially with their own or similar species. This "shark" will get along with some of the loaches (
Botia sp.) but other bottom fish should be avoided. Upper fish such as the medium barbs, rasbora and danios would be suitable. In a large aquarium (6+ feet) a group of 6 could be attempted, but any fewer would likely result in the death of subordinate fish within the group.
On the Five Banded Barb, if this is the species
Desmopuntius pentazona, it is a soft water species. More at SF:
www.seriouslyfish.com
On the matter of community fish with gourami...gourami are sedate fish and should never (with a very few exceptions) be housed with danios or barbs. Rasbora are fine [or some of the quieter peaceful characins (tetras) if you move outside SE Asia]. The loaches and "sharks" can be trouble here too, though not all species.