I was JUST reading an article about CrossFit and how you shouldn't do what everyone else is doing when you first start out! That's true for most exercise--you need to start slow to develop the correct form and learn the moves. I think doing 4 box jumps is great. It's 4 you wouldn't have done last week! You're breaking out of your comfort zone and that's to be admired.

I am easing my way into running and I have been told over and over: go SLOW. I know from experience trying it in the past--doing too much, too soon is too hard and leads to injuries or burnout. You're developing new muscles and settling into a new routine. Good for you!