Nick Mohammed is actually playing the violin. Not only that, is his own personal violin from home. His wife of 14 years Becka is playing the piano accompaniment.
The Canadian football announcers are voiced by Ryan Stiles and Colin Mochrie, best known for their work on Whose Line Is It Anyway? (1998).
When offering advice to Rebecca, Leslie warns her to beware of a Willy Wonka & the Chocolate Factory (1971)-type scenario. When Akufo arrives at the meeting, he's wearing a purple suit, much like Willy Wonka's.
The book coach Beard is reading is Finding the Mother Tree: Discovering the Wisdom of the Forest by Suzanne Simard. It is an autobiographical account of her role in developing the theory that came to be known as the "wood wide web," which is about how trees communicate and share nutrients to support each other, a distinct contrast to prevailing theories that trees, and maybe even other organisms, primarily compete.
When Nate takes the hat and colorful scarves out of the closet at his parents house, they are the typical kerchiefs used for Magic tricks, a reference to Nick Mohammed, the actor who plays Nate, who does magic himself.