Academic pipeline: How many papers should you have under review?
You're simply asking the wrong question.  Your goal should be to do the best work you can, not the most — quality, not quantity.  One revolutionary paper is worth far more than dozens of incremental papers that nobody reads.

To put it another way, if you find yourself submitting so many papers that you're worried about being overwhelmed, you're doing something wrong.  Aim higher.  Publish fewer, bigger chunks of work.  Spend less time writing and more time thinking and digging.  Stop just writing papers and develop a research program.  The CV bullets will take care of themselves.