I have 8 Tiger Barbs and they are very PLAYFUL, but they do not cause chaos in the tank. Make sure you have plenty of them in a group, at least 6. I doubt that they will reach 4 inches, but you never know.
Its a good buy at WalMart - AquaCulture 29 G Deluxe, but their light/hood sucks. If you want a better light, go get one. If you want a better hood, go get one. You can always get something better and give away what you had with the box. The AquaTech filter in the kit, you can give it away and get a better filter. Its all up to your preference.
Thunder