Having checked all of the above in "what should be considered" I still have some others: zoning, predators, and theft have already been mentioned, as well as knowing to choose a healthy animal. Food costs were listed but keep in mind other costs: feeders and water containers weather and need to be replaced. Fencing needs fixing, and tools to do it, as well as cage repair. Dewormers, antiseptics and other health care items regularly needed also run up a tab. When considering how much space you have for your livestock include how much space you have for storing feed, especially hay/straw bales. In some cases manure needs to be hauled off and some dumps charge by the pound.
Being prepared is way over half the battle, the rest is just a little hard work and the will to do it.
Most of all, Recycle, Relax, and Enjoy your critters!