Yes, that actually is somewhat normal for all bats. Manufacturers use an adhesive glue to secure the end cap onto bats, and over time a small piece of the excess glue can flake off and sound like a very small pebble. Sometimes this happens after 100 swings, sometimes after 1000, but it happens to almost any bat eventually. As long as you aren't seeing any performance issues, I wouldn't worry about it too much.
Bats are only going to have so many hits in them and bats that are consistently used by the entire team definitely run the risk of breaking prematurely over a bat just used by an individual. To get the most out of the 2018 Louisville Slugger Prime 918 BBCOR Baseball Bat: WTLBBP918B3 we would not recommend using it as a team bat.
Yes, we highly recommend a break-in period before game use since this is a composite bat. We generally recommend 100-200 swings off a tee or soft toss, rotating the bat 1/4" each swing to get a nice break-in all around the barrel on composite bats.