Hi and welcome to the ball python world!
For feeding, I prefer live. My live feeders seem to have stronger feeding responses and I don't have to deal with the mess that comes with thawing out ~15 rats. It's really just personal preference.
I think it is a great idea to start off with a morph, single gene or otherwise. I don't think the market for spiders, pastels, or any other single genes is going anywhere like a previous poster insinuated. If you do get hooked (like most of us have!), you'll have a nice starting point.
If I were you, I would get my first one from a breeder. You'll likely get a health guarantee of sorts, someone to answer and questions specific to your animal and a better deal than you would at a pet store or a pet store animal on Craigslist.
It sounds like you and your daughter will fit right in, I can't wait to see pics of your new addition when you pick it out![]()