I will answer your questions the best I can...
..."Let me say that this would be my first snake..."
Good choice, my first too, and I would have regreted not getting her, she changed my life in many ways, and I know how cheeesy that sounds, but it's true.
I am wondering if they will strangle you or anything?
NO! Well I can't say that for sure, I guess if you had a REALLY big and strong ball and had them around your neck and start plucking scales there MIGHT be some strangulation but probably a bite too, but woulden't you? on a serious note, ball pythons (expecially CB) are really docile wonderful snakes and don't really even get big enough for a grown person not to be able to overpower it.
..."Also, I heard that it is good to try and feed them, outside of their cage, to avoid impaction, and so they don't snap at your hand, thinking you are about to feed them, if you just want to handle them"...
This is a prefrence, if you are really afraid of being bitten or are using a loose substrate I would feed out of the cage...
If you are using newspaper for a substrate you CAN feed inside the cage, and most likely won't get bit unless you forget to wash your hands before putting them in the cage or you scare them. Most ball pythons WON'T bite! Some do when WE (not the snake) make errors.
..."I am also wondering, if I am allowed to let my snake roam around on the ground, as long as it is under supervision?"...
As long aas you keep a close eye on them I think it is ok for some good photo shots or just some sun.
Also, do they need to have the heat light on, even during the night?
That depends on how you heat the cage. I would suggest for one snake getting a UTH and maybe a red heat bulb. Keep your temps right and your humidity. You seem to have read a few care sheets, so I am sure you know the humidity and temps, if not post those questions on here also.
..."The guy at the store told me that I shouldn't use astro turf, and told me that I should use cypress mulch. Are there any reasons for this, or would that be a good idea?"...
Astroturf is not good, the fake grass can irritate the snakes scales and skin. Mulch s OK but stay away from pine and ceadar, Newspaper is a good substrate as it is cheap easy to find, and easy to clean.
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"Wanting to be someone else is a waste of the person you are." - Kurt Cobain
"It is better to be hated for what you are than loved for what you're not."
"You laugh at me because I am different; I laugh at you because you are all the same."