>>Should I use a humidifier like I did with my lizards?
No - proper caging a water bowl and decent substrate should be enough to maintain proper humidity for a ball (around 60%)
>>What is a good lighting/heating system for a ball python?
Balls are nocturnal and do not need lighting. An appropriate size under tank heater will work well in maintaining the proper ambient temperatures (82*)and provide a good warm spot (90*). Please be sure you put it on a thermostat or rheostat so it doesn't overheat.
>>They are all together in the cage at the pet store, would it be okay to keep them together in my home?
Pet stores really suck at providing an optimal environment for their animals - it is more economical for them to throw a bunch of animals in a cage instead of providing for them properly. If you are getting a pair of hatchlings then there shouldn't be any problems with temporarily housing them together - you will need to take them out and feed them seperatly tho. Eventually you'll have to have them sexed and possibly separate them depending on the results. As for petstores - please be aware that you most likely will be getting captive hatched babies that were born in Africa and shipped to the US - they may have a variety of issues that don't really make them ideal pets - you may want to consider buying a captive born snake from a breeder.
>>If it is okay, and I got a second later on, could I keep an adult and a hatchling together?
NO
>>Is a male or a female better for someone new to snakes?
Doesn't matter
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Tosha 
"Nihil facimus sed id bene facimus"
7.33.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Anakin Skywalker)
0.0.1 Green Tree Python (Verdi - yeah I know but my kids love the book)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Desert Tortoise (Pope John Paul aka JP )
2.2.1 Fish (1,2,3,4)
0.0.2 frogs rescued from pool skimmer