How many verses ? As many or as few as are required for you to tell the story.

I'm reminded of seeing the great Steve Goodman at Cambridge Folk Festival, 1972, I think. He sang his great song "The Ballad Of Penny Evans" - a masterpiece, in 6 verses.
Soon after he sang his "Ultimate Country and Western" song. From what I recall, he said by way of introduction that every country song had to contain one or more of 5 elements - momma, a truck, the farm, prison or a train. The song went something like :

"Ever since the day that momma went to prison,
Things on the farm ain't ever been the same.
We were sorry on the day she got her freedom,
'cause she drove the goddamn truck into a train".

So, 6 verses or 1 - whatever it takes.

The longest song I ever heard sung live was at the Ballisodare Folk Festival in 1978, on the main stage as well. Over 25 minutes long - he was pushing his luck more than a bit with that.