When considering whether or not to keep chickens you have a choice of how to begin. You can start with eggs (which take time to incubate and have the possibility to come with male/female mix), chicks (minimum of 25 to keep each-other warm during travel), or you could go for the mature layer (more expensive of the three options).
As far as feeding goes, chicken feed is available but I would say let them eat what is in your yard along with vegetable scraps (feeding pullets puree), after all having chickens is all about sustainable self sufficiency.
The benefits of raising chickens are numerous. Free range chickens lay healthier eggs. They keep garden pest populations down. They till the soil and there poop makes for great compost. It is also a way to preserve breeds. Once they no longer lay eggs they can be used as food if you can handle the slaughter process, you can sell them or just keep them and let them pass into the great beyond naturally.