Hello,
Welcome to the jam. I do hope you will enjoy it.
Sound and music is permitted (and optional), but dialog is not permitted in the sound and music. The game should be able to be completed without sound, so don't encode hints and clues into the sound effects.
Remember that you should only use music and sound for which you own a license.
To properly attribute assets you use in the game, there are multiple ways, but the simplest is to embed any attributions in the "notes = " section in the game_information {} section. Typing CREDITS will reveal all the embedded credits, which is the only breaking of the fourth wall that is permitted when playing the game (as to its word count constraints).
Chris