First, mice and then rats are fine. I wouldn't feed ASF as BP's can imprint on those and they can be hard to get, as mentioned.
Don't feed too big a meal as explained. Try to get your snake on F/T for your sake, and more importantly, your BP's.
Mistakes people make:
1. Wrong temps or humidity. NOT getting a thermostat - which is a must. Also not properly checking temps. IR temp gun for ground temps is a must IMO.
2. Handling too much. Let your snake settle in. Get a few meals in. Then start gentle handling sessions - short ones. A few minutes every few days to start.
3. Anthropomorphizing. Your BP is a snake, not a human. Learn what makes snakes tick, not what you think your snake wants.
4. Not enough or proper sized hides.
5. Getting too many snakes too fast.
6. Not properly quarantining new additions. This must be done ALWAYS and for any new addition after your first.
7. Going for tank setups that humans think look cool, but are not best for your snake.