Hi and welcome to BP.net!

First off...I would NOT get one from any pet store. The risk of getting an unhealthy snake that can't thrive is too high. Not absolute...but high. There are lots of great breeders that can ship you a very healthy, high quality captive bred animal for about the same price you'd pay for one at Petsmart. Also, if there are any herp shows/expos in your area, you can look there. But you still need to do a little research ahead of time to know a little about the vendors and what to look for.

Second...it's perfectly fine to do routine cleaning and maintenance on the cage. Once the snake is settled in and used to its routine, such things don't add any undue stress.

Third...I don't think a rock is necessary at all. An under-tank heater is best to achieve a proper gradient and basking spot...but even with just an overhead lamp...if you can get the right temps and keep your humidity levels at the right spot...that's enough for the snake. It doesn't need a rock or anything.

Lastly....be sure to check out our caresheet!

http://www.ball-pythons.net/modules....warticle&id=52

Tons of good info in there!