Your setup should work. My wife rode across the U.S. using only a pair of Ortlieb Front Packers (used on the rear rack), and her camping gear carried on top of the rack. She has graduated to full sized panniers now, and uses Ortlieb Packer Plus panniers
Her bike handles very well with the load she carries. She has pulled away from me on the downhills when my computer was reading 45 mph with her present setup. She has about 22,000 touring miles with this setup without any significant issues. Try your bike with a rear only setup and see how it handles. Our daughters use Ortlieb Back Rollers, and do not have any problems with wobble, etc. All of use an Ortlieb Rackpack to carry our camping gear. The girls are not light packers!
I prefer to divide my gear weight between the front and rear of the bike. I carry the tent, and cooking gear so I need a little more room.
The one problem I have seen with the weight in the rear is the bike is harder to lift over curbs or a during a similar action. Once the front wheel is lifted, maneuvering it by hand can get squirrelly. The daughters ride Long Haul Truckers, and my wife rides a Co-Motion touring bike. I think the 520 would be as stable.
Two moths in Europe.