Some groups in Taiwan teach chaquan #5 and #6 as well.
The full chaquan system seems quite huge in China, including many sets of tantui, huaquan, etc. as well, and also lots of weapons sets.
Chaquan sets #1-#3 seem more basic than the later ones; maybe that is why others skipped to Chaquan #4 first.
In modern wushu today, you can see substantial parts of Chaquan #4 just spliced into the "changquan" routine. (I also only learned #4 myself.)
https://www.youtube.com/watch?v=fFjfl87ZjNcJohn: I also wish I knew what the application for that movement was...