About once a week or more for hatchlings. For adults it can be significantly less. Impaction is rare, so don't sweat it.
50 grams of food per week in an 850 gram snake is not totally unreasonable, but you safely could do more. Try about 10% for starters if you feel the need to feed more. You could start with one small rat ~60 grams, an adult male BP will never need more than a small rat. BPs can be imprint feeders so he may insist upon mice.
You may start your own mice colony and beef those mice up a bit more before feeding them off, just a thought.
Also, put them in there one at a time so the other mouse doesn't hurt him while he constricts the first one. Rodents can be meanies when they get the notion they're about to be eaten.
JonV