My (personal) ideal tiger barb tank would be a 33 gallon long. It's the length of a 55 gallon but only about 12 inches tall. Basically if you laid 3 ten gallon tanks end to end, you would have a 33 gallon long. This could easily handle a school of 11 tiger barbs and a couple of BN plecos. You could even do like six of the wild type (striped) and five of the green morph or something like that. The 48" length is great for how active they are. The height of the tank makes lighting easy for planting as you don't need high powered lights to get through a lot of depth of water. You'd have a lot of options of plants in something like this.
If you want other tank mates, I'd recommend a 55 gallon minimum. A good size school of 11+ tiger barbs. A good size school of another medium tetra or barb that are hardy and active, something like serpaes or silver tip tetras. You can easily do a school of cory cats as well. If you get a good size school of tiger barbs they aren't super nippy with other fish. You could even add a center piece fish like a single medium sized SA cichlid (convict, keyhole, salvini, severum, etc). As for plants in something like that it really depends on how complicated you want to go. I always recommend Anubias, Cryptocoryne, Java ferns, and moss balls. They're easy to grow, hardy, and most species don't require anything too specialized.