On the left, below PLAY NOW, you should see all of your friends with options to sort them by status (blue, green, red, grey), name or average. They will be hidden from game invites unless they are publicly green. Your current no. of friends will cause deviations though.
The 255 limit has been reported here numerous times. It's arbitrary but logical in the computing world because it's one display of a Byte or 8 Bit, 2^^8 -1.
Once this threshold has been surpassed, problems arise so that you don't see all plus you can't address some in PM and game invites and whatnots.
I for one obey to the limit of 100 friends. I can't care about those (or more than that) and I once heard that it influences the game in a negative way. For sure, more friends produce more alarms during the game when they are going online or offline.