Agree with FSP - you’d be happier with a small mixer rather than trying to use the BB to add an mp3 player into the mix. Behringer sells a couple of cheap small mixers that have worked really well for me.
Regarding your samples, you could add one (or maybe one for each loop in a sing) to each song via the BB as an accent hit but they will have to be short. I don’t recall what the size limit is in the BB for accent hits.