Joe Conley and Eric Scott actually formed a real-life song and dance act, much like what is depicted in this episode, and took it on the road. They sang popular songs from the 1930s to the 1970s. They also recorded a record album in 1979 which included a version of "The Waltons" theme song with lyrics.
Mary Ellen brings Mike home with no preparation or modifications for a person in a wheelchair. No wheelchair ramps. Only bathroom is upstairs inside. Of course, in 1940s, indoor bathrooms weren't everywhere.