Then a rainbow BTA it is!
There are no guarantees with any of your prerequisites. For example, with BTAs:
1. Colorful - yes, unless bleached or unhealthy
2. Does not split too often or grow too big. - They typically don't split often unless it's stressed or you have one that's known to constantly split. If you don't feed it a lot, it won't grow too big
3. Hardy ??? - Yes, when you give it the proper environment
4. Will not eat my fish - it usually doesn't eat fish, and if you have a clown pair being hosted by the BTA, they usually do a good job of keeping fish away.