Probably start at NSR s it is the longest pipe, I have always removed as much of the old fluid from the reservoir prior to starting to pour in new fluid and plan is to flush enough fluid through that first bleed point to clear the reservoir and longest pipe of old fluid plus a bit more, I probably just do the same for the OSR again flushing enough fluid through to clear all the old fluid out, then finish with doing the same for the front brakes though they don't need so much fluid flushed through. There will always be some trapped fluid in the ABS block so unless you have VCDS or equivalent to perform a flush that will stay and mix back in to the old fluid along with the clutch fluid, but both these extra sources of old fluid are quite low volume so the overall "sharing" of the extra moisture will not make a huge difference especially if you replace the fluid every other year.
I tend to just use VW Group brake fluid for no amazing reason, it does the job and is okay price wise.
