In the squad room, Beckett is wearing a brown two-button jacket when she gets the call to go to the morgue. In the next scene in the morgue, she is wearing a green zip-up jacket. When she returns to the squad room, she is again wearing the brown jacket.
When Castle finally gets the murderer to crack in the interrogation room, he does it by asking the guy to play a difficult bass line. If you look at the page of music, it's written in treble clef, not bass clef.
Allegedly, the DEA can't bust the "church's" pot farm because of "freedom of religious expression." That claim didn't work during prohibition (churches were stopped from using wine for communion), and it doesn't work today. The Supreme Court ruled in several cases, most involving polyandry, that freedom of religion does not guarantee freedom of practice. Or, as one judge said: "Freedom of religion does not include the right to burn heretics."
At the end of the episode when they are jamming, it's very obvious that Buck/Hank has no idea how to play bass, not even "playing" to the beat of the song. Keith, behind him, is not playing the song but at least is playing actual chords.
The "roadie" is Hank Rodgers. Martha's last name and Richard Castle's original last name is Rodgers. Hank is no relation to them, but no one mentions the coincidence.