I have never heard of catappa leafs... Looking up about them, it seems to be an Indian Almond Leaf?
Found an article here about it, although it mentions nothing about goldfish- (Link is not visible to guests. Please register to view.
I really don't know if they're goldfish friendly
I'll post in another forum I belong to, tomorrow about it, I'm sure someone there might know
As for live plants, a pot with some aquatic soil and large rocks on the top would be fine, or if you have suitable substrate that the plants can grow their roots in that would also be fine
What plants were you considering? As goldfish will eat most things