it depends if u wanna feed live or pre-killed/frozen prey. if live, u gotta buy local. research a local breeder or pet store that carries live rodents. if u wanna feed frozen and thawed prey, u can buy these local. or u can buy them in bulk from online retailers like Rodent Pro, Rodent Plus, Big Cheese Rodent, etc. and they will ship them to your door on dry ice.
IMO feeding the BP at dusk or night when it's out of it's hide (or peeking out) is best. pick a day of the week to feed and u may adjust as u get to know your snake more. i.e. like when it's most active, feeding every 5 days vs. once a week, etc.
also if you're starting with a baby BP, it's best to start it in a 10-20 gallon tank if u are going the tank/vivarium route. move them up to the next size as it grows.