I think the best option for a new snake buyer is to visit a reptile expo. That way you can see all the amazing morphs that are available, and you will have more than one animal to choose from if you still want to go with the butter morph.
Also, a breeder at a reptile expo will be able to give you detailed information about the animal you want to purchase, while a pet store likely won't have the experience or knowledge that a breeder does.
IBD in ball pythons doesn't tend to incubate long. The symptoms show up early and are severe. Boa constrictors can incubate the virus for much longer without showing symptoms, but IBD isn't as common as you might think.