in fact, there is no specific rule for the number of keys in your timeline.
the most effective way is to find some references for your motion you want to do.
let's say, you want to do a jumping motion.
then, it is easy to be an actor by yourself.
you can capture your jumping motion by your DV.
thus, you may do your motion with your captured video.
even, you can import that video reference into viewport background as a starting.
certainly, it is for beginners.
hope this help.