To start, some basic Taxonomy for you:
Class:
Actinopterygii
Order:Cypriniformes
Family: Characidae
Size: Length: 8 to 15 inches (20 to 38 cm)
Weight:Up to 3 lbs (1.4 kg)
Diet:Fish, birds, reptiles, rodents, small mammals and sometimes carrion
Distribution:South America
Young: Several thousand eggs at a time
Animal Predators: Unknown
IUCN Status:No special status
Terms:Young: Fry
Group: Shoal
Lifespan:Unknown
As far as how long your 29gal. will last you - expect to upgrade fairly soon. No they do not get "Huge" so to speak, but since they are voracious eaters, and spend most of their time constantly searching for food, they require a decent amount of open swimming space.
--Em