From what I gathered in TV, it seems that 友達(tomodachi) is like a general friend while 仲間(nakama) is someone you go through thick and thin with. An example is in One Piece, where the crewmates call each other nakama. I have also heard it used with bandmates. As for "or," か (ka) can be used, such as 田中さんや山田さんはやります。 (tanaka-san ya yamada-san wa yarimasu) (Tanaka or Yamada will do it)

Curious as well! Always thought nakama was more of a partner/colleague than a friend but let's see what the good nihonfolk say