Breeding is stressful in the sense that the typically do not eat during the process which means you have to get them to a healthy weight to handle breeding then after the process is over you have to get them back up again. Much less of a big deal for males usually but for females it can be hard on them.

I am new to the bp scene but I bred gtps about ten years ago along with others. Some species are less affected by it such as african house snakes which I just left together all the time. They ate just fine and seemed to know when they were Ok to breed. They are one of the most prolific species of snake in the world for a reason. They are inexpensive well mannered and hardy. An excellent choice when you want to learn the process so you don't loose a bunch of eggs due to inexperienced incubating practices.

As far as the genetics, I am new to that. Previously I only bred normals, gtps were valuable enough alone at the time. There are some great calculators that will tell you what you will get by breeding certain morphs together. If I get time (and my pc) I will post links to them for you.

As for breeding siblings, not sure of the ramifications of doing that with snakes, I never did I because I had seen the issues it caused with other species. Maybe someone more knowledgeable than me on that can chime in.