I was wondering if there was a minimum number of songs to show a custom genre in the genre tab? If there is not, then some of my genres do not show up (Thanksgiving, Halloween, Wedding).

The Genre Tab brings up a menu that shows your top 20 genres which have the most songs. So if a genre is not showing up on the list - it just means there are 20 other genres with more songs than that one.

You can always type in "Thanksgiving", etc in the search box to list the songs with that genre.