I used to own a Weesatch. Brassburn is right on about the plates. If you want it to truly fit right, get plates. The Hydro pack will work too, but only until you drink all the water. As you drink, the weight does start to shift forward. If you go the hydro pack route, I suggest an external pack rather than placing a bladder inside the rear panel. The reason is that the tension of the waist strap will be on your body and the bladder. As you drink, the bledder shrinks and the waist band losens. The straps are not easy to adjust by yourself when wearing the rig.
As far as pouches go, think thin and streamlined. You are placing more pouches ontop of what is already a double mag pouch. This will make the rig stick out a lot! The temptation is there to cover every inch of real estate with pouches, but you will soon end up with very ungainly results. I work out a lot and have a large chest and thin waist. My Weesatch made me feel like I had a huge gut. I found that keeping things streamlined was the way to go. Pistol mag pouch, small IFAK, and admin pouch was all that ended up on the front of mine.
Again, Brassburn is right about the enhanced straps. They are the tits! Also, invest in the shoulder strap pads. You will thank me later.