The question isn't how many, but "how good are they?" Some judgments aren't any good. The person is broke, on mom's couch, or something else. You want what I call the "better debtor." That's the person who has the money to pay, but won't. Or, doesn't think anyone knows how to get him to pay.
Now, to answer the question: 4 judgments a month (if they are good!) at just $5,000 each, gets you $120K a year.
So, you don't want a lot of judgments. You want to know
1) how to find judgments online,
2) how to identify the good ones, and
3) how to then enforce them.
You should be spending 85% of your work time (however much that is when you start) looking through judgments, mostly online. I'll show you how to ID the good ones, using one or more of the professional databases that locate assets.
Questions? Let me know.