I’ve just added a third. Is 4 too many?

It totally depends on your weight and riding style.

I had three, dropped to two – might go back to three.

I dropped one from mine (to 1) – too progressive for me I found. I had to run them really soft to get a decent amount of travel on proper terrain, so one less works well as its still pretty progressive, just not overly so.

Had 3 in mine, was running loads of sag and still couldn’t bottom them out!

Have since dropped to 2 and added 5psi to compensate, this seems to be a pretty ideal compromise where the fork is still really supple off the top but has plenty of bottom out resistance.