Scott,
I’m running MC8 on a Retina MacBook Pro with OSX10.9.4 with no problems whatsoever. I was having the same issues you describe, i.e. having to start MC8 2 times to get it to finally start completely.It was also running very slowly once it was up and running. At the time, I was running OSX10.9.2. When I upgraded to 10.9.3 via the Mac upgrade, the problem persisted. I ended up downloading the full version of 10.9.3 and reinstalling the OS. That fixed my issues. Perhaps you could download the full version of 10.9.4 and install over the top of your present installation. Maybe that will help.