Looks like I'm late. Haha.
I was previously on a belt system, but now I find it much more convenient to lug a TT Change Up loaded with my lenses, and my body separate. Using any decent big bag (doesn't even have to be a camera bag; I went on assignment with a Crumpler messenger bag before), the CU goes in, with the body +grip in a Skin Chimp Cage.
The CU will fit up to three lenses inside. It will take a 70-200 f/2.8 with hood reversed, or 24-70 with hood in place. The height of the bag will not enable you to fit a 70-200 with hood in place, unless you are comfortable with it poking out of the zipper. I leave the zipper permanently open. Nothing has fallen out.
You will notice there are two stretch pockets on each side, and two more on the front. I use the side ones for a Speedlite + Sto-fen (if I need flash on that shoot), and the other side is used for a Lenspen and a torchlight.
The two front ones are used to keep biz cards, mints, and spare batteries (easier access than a zippered compartment). I usually use the front zippered compartment for unimportant stuff, as it's not as quick to access. To the rear of the bag is one zippered slim compartment and one open slip-in compartment. I use the slip in compartment for a small notepad, a pen, and my cell phone. The zippered compartment is useful in stowing bounce cards (or other slips of papers).
I haven't found myself having to add more pouches on the modular rails on the belt. Carrying that much gear already is quite tiring, and your waist will thank you for packing as light as possible.