I am working through this exercise and wanted to know if its generally a good practice, in the arcing ball bounce, to have an even number frames in the arc ascent and descent?
Yep. Especially when you are learning. It will make it a lot easier.
Later on, 'in the real world' of animation, it might not work out so neatly, but you will know how to handle those situations by the time you get there ;)