^^^ what buffalo said, the more the merrier. The more you have the more natural, less shy they'll act. Kind of like if I went to a party or something and didn't know anyone, I'd be a little more reserved than if I had 4-5 friends with me. Are they going to be by themselves or will they have tank mates of a different species? On the bright side, with just a couple you can get them used to hand feeding so when you add others, they'll see the original two eating from your fingers and pick it up right off the bat. Good luck, don't forget pictures!