6 would be great. They are hardy little fish. I kept 2 peppered corys in my first tank even 12 years ago. They did great and I had no clue what I was doing. I how got 5 for my 55 gal tank. They are great just as I remembered them being. It will not be too busy. They hide out and you can't see them at times. Then when the food falls they get right to work.
I personally Love the peppered corys. They are cheap can be easy to breed and I love the blotches. But that's just me.