This was my understanding, too (maximum 4 programs, which, in the latest released version, are already set up). I, too, read it somewhere. BUT, I just went in and created a 5th program. So I'm not sure why there is a limit stated in the documentation, or whether my newly-created 5th program will cause issues down the line. (@harald might know, but he's likely unable to dive into the "why" right now if he doesn't.)
If it turns out that only 4 programs are the maximum recommended, you could get around that program maximum by setting up multiple programs under multiple organizations. But multiple tenancy, which I set up last year, was trickier to set up and to manage. Happy to share my notes on that if you'd like, but I am glad I'm setting up all programs under only one organization this year!