It would be almost impossible to find a list of all the country songs released in 1973, but the Wikipedia page I've linked below gives all the most important songs from that year.
Click on the related link for a list of country music performers.
Definitely NOT No! Not at all.
country,some pop,rock.......but not all music
There are numerous reputable websites that provide lists of songs that are considered country classics. All Music is one online company that provides such lists.
No its for all types of music
Appalachian
Appalachian
Rolling Stone maintains an on-line list of all their covers.You can find the 1973 covers by following the link, below.
Appalachian mountains
Nashville Is home or "Birth place" of Country music it is importantly noticed to all country singers. Today, there are many recording studios in Nashville that produce Country and other kinds of music.
I don't believe you can list all black country singers, any more than you can list all white country singers. One has to remember, that this would include independents as well a major label singers. Since the Indies grossly outnumber the majors in any music genre, as well as country, some are bound to be ommitted and overlooked. But all is not lost. If you can find a copy of Pamela E. Foster's 1998 anthology, "My Country, The African Diaspora's Country Music Heritage" you'll have a leg up on most. This 340-page book with a complete discography shows that Black Amerians were involved in Country Music from the beginning as singers, songwriters, publishers, etc. ISBN-0-9662680-1-6 Joe Arnold, Roughshod Records
Popularity is a tough thing to judge empirically, however most people who like country music would proabably put Johnny Cash pretty high on the list. (IMHO)