If there's a limit, I haven't hit it yet. I've been accepted by (i.e., I'm technically a writer for) about 50 of them, large and small, and have written for more than dozen or so. If you write on a range of topics, it's a good idea to get accepted by as many pubs as you can as long as you *might* write about their subjects at some point. That way, if you suddenly write about a topic you hadn't planned to deal with, you'll have an appropriate publication waiting for you.

I've found that the greatest benefit comes from writing for pubs with a highly engaged following--that is, with followers who love the pub and read and engage regularly with stories on it. But you may have to write for quite a few pubs to figure out which ones have followers who will engage with your subject. Good luck!