I can't say for certain that all BC FDs except HHI FR are dispatched on 154.355, but I believe they are. Someone else may say otherwise.
Yes, 154.355 is a rebroadcast of the dispatch talkgroup on Palmetto P25.
Each FD has their own tac channel. Many of them are encrypted. Most traffic takes place on the dispatch talkgroup.
Yes, EMS dispatch is encrypted.