Chris Swindle is the voice actor who plays Po's dad, Li (originally played in Kung Fu Panda 3 by Bryan Cranston). Swindle is also known for voice doubling for Philip Seymour Hoffman, Adam Sandler, and John Goodman.
The "Four Symbols" are four mythological creatures in the Chinese constellations. They are the Azure Dragon of the East, the Vermilion Bird of the South, the White Tiger of the West, and the Black Turtle of the North. Each represents a direction and a season, and has its own individual characteristics.
Dry Salty Plums is a delicacy in China where it is known as huamei. It has a strong, distinctive flavor, and is often said to be an acquired taste, which the show writers can attest. (They purchased several bags of them to try; most of the bags remained in the writers' room, unopened, throughout the duration of the yearlong writing period.).