Interesting to note that I would start with just tossing one ball from hand to hand - as soon as you can do that consistently, try two (as in left, right, catch, catch, right left, catch catch, etc). again do that until they look the same in both directions and the heights stay the same and you don't drop them. Then go for all 3, usually starting is the hardest part, and you'll try it a few times before you get the first throw decent.
Sometimes you have to have people stand right in front of a wall to teach them not to throw forward...
I taught myself while home sick from school - took about a week. This was pre internet and I had no references at all other than 3 balls.
3 seems the smart choice to me.
"The number of Unix installations has grown to 10, with more expected." -- The Unix Programmer's Manual, 2nd Edition, June, 1972