Do you mean pairs, because the maximum nests a person can have is 5 ^^
In terms of starting a hatchery, you'll need banners/cards/appropriate advertising.
This guide is pretty helpful.
In terms of pairs, most anything that
isn't basic or horribly ugly will sell. However— Nocturnes/Crystal/Facet/Iridescent/Shimmer/Coatls have all sold quickly and easily, in my experience. Of course, having a hatchery doesn't automatically mean hatchlings will sell, it's all just about patience, when it comes down to it.
Make a hatchery ----> Slowly Build Pinglists ----> Hatchlings/Dragons will generally sell better