It sounds like you're pretty close to your prime nirvana already. Add one lens based on the advice above (
RLPhoto,
Neuro) and you're golden!
I think everyone that is a serious photography freak eventually starts down the path of "I want a great prime kit" with their FF camera. It's kind of like buying a boat. So go ahead and buy the extra primes, shoot and enjoy them, build your skills and eventually you'll probably get it out of your system.
I don't mean this in an insulting or bad way, it is just an honest observation. I did the same thing. But once you get past it, you will either become a dedicated and life long prime shooter, or you'll decide that the new zooms that Canon has released in the past few years are so good that it's not worth the trouble keeping up with all the extra gear.
The middle ground is if you divide up your shooting between thoughtful art shooting and busy event shooting. Primes are wonderful for those times when it's "just you and your craft". But unless you have a solid method and workflow set up for certain events to carry and use the extra primes, or you shoot portraits/babies a lot, I think the primes will eventually gather dust.
Personally, I tend toward the wide end. I have the 24L-II, 28/1.8, 50/1.8, 50/1.4, 50 Macro. I used to have the 135/2 and the 35L. I have loved all these lenses but I honestly don't use them that often anymore. It's just easier to use the zooms and the pictures are still phenomenal. I still use the 28/1.8 for low light campfire shots, etc. And for some reason, I've never found a groove for the ever popular standard 50mm FL.
In general, the 16-35L, 24-70L and 24-105L stay on my cameras 90% of the time and work great for my needs. For swimming it's often the 70-200L or the 70-300L and maybe the 24-105L up close.
I'm looking forward to seeing what you decide!