I recall Hootenannies in school gyms and church halls in the early sixties.
We (the performers) would all get together for a meeting before the shows and make sure that no songs were repeated. If this were not done, we might have 4 or 5 renditions of "Don't Think Twice".

In order to decide what is a folk music instrument, we'd have to agree on what is "Folk Music". Folkies have been attempting to define this for decades and have not yet decided on a definition.
-If we know who wrote it is it folk music? I recall wearing a Shelter Valley Folk Festival to a Toronto folk club and being told, "Shelter Valley is not a folk festival, it's a singer/songwriter festival."

My favourite instrument is the acoustic guitar, and I use it for many genres of music.