I would bet against him being able to learn three balls.
But he was very dedicated. Long story short. After many years he could comfortably juggle 6 (six!) balls.
It looked wobbly, he still looked like a person without coordination, but the balls somehow stayed in the air.
Greatest pride was catching a tumbling beer at a party, and getting called spider-man.
Getting good at juggling makes things fall down noticeably slower. But despite getting really good at juggling, I haven't observed any other super powers.
You can do four-out-of-five, which is a five ball cascade with a missing beat (just as how you learned two-out-of-three while learning initially). Unfortunately it's very hard and still doesn't impress people.