You don't buy the 17-55 if you're going full frame, as that lens is an ef-s and won't fit a 5d.
The 24 II L you don't get because of the superior IQ alone, you buy it because you get an f-stop of 1,4 instead of 2,8. It's the sickest piece of wideangle glass out there. And yeah, I have the 14 L II as well, but the 24 on my camera (1,3 crop) gives it roughly the same length as a 35 L will give you on FF, which is extremely useful lens. But for portraits? Nope.. You would use a 70-200 for example for general purposes and also protrait. The new 70-200 is the best zoom-lens ever made and it's scary sharp edge to edge on FF and VERY sharp wide open through all focals, no CA, and BLISTERING fast AF. Which makes it useful for everything, not just a specialized protrait lens.
If you want a lens just for portraits, the 85 L will do it better than any other lens. I traded mine for the new 70-200, but I have the 24 L II and the 50 L for lowlight and portraits.
Many people buy the best lenses because they think they will get better pictures, which is very untrue in many cases. I'm not saying you do, but you should really get a proper light-setup and learn how to control light and balance ambient and flashes when you want to go more into protraits. I have never heard or seen anybody taking professional portraits without having absolute awarness and/or control over all the light hitting the subject. A flat and boring light-portrait taken with a 5d2 and 85mm f1,2 L will give you crappy results anyway, compared to having a 350d with a 50mm f1,8 and proper light setup and full control. If you see a billboard with a hot chick in a commercial, do you wonder what lens they used or do you think, "wow, that's such cool light" ? ( I would say, wow, hot chick, though