If you want 6 hens, maybe choose around 18 eggs, which will account for shipping problems, infertility, incubation errors, chick deaths and the normal cockerel/pullet split.
Black Sumatras are not the cheapest birds around, and aren't always easy to find. They are also more independent, flighty and may not handle confinement well, based on what I have read. It may be better to order a dozen or so Barred Rocks, Easter Eggers, Buff Orpingtons, Australorps or Marans. These breeds are great for novice chicken keepers, and handle confinement well, are very friendly and are good - great egg layers. A bonus is that they are relatively easy to find. You could hatch some of these, see how you like chicken keeping, and them maybe branch out by hatching a half dozen Sumatra eggs (hopefully resulting in 2-3 pullets).
While some people will not do this, you could butcher the cockerels for meat (all the "easy" breeds I mentioned do get some meat on them, except perhaps the Easter Eggers). Also, you could put ads out for them to sell cheaply, or for free. Please know that they will most likely be butchered, but there is a small chance they could be kept as a flock rooster, possibly in a rural area near your hometown.
Hope this helps! Enjoy your chicken adventure!