I don't leave dark periods before harvest. I used to do it all the time but since I stopped im getting far less bud rot. I would get rot every single grow just about, now I get much less and to be honest I don't think it makes any difference to the final product. the buds will continue to ripen after you chop anyway.
I hang stems or whole plants depending on the plant size and the location im at. I stopped using drying racks a couple years ago and now I see a far superior product. the buds just dry nicer and a little slower which isn't a bad thing. I dry in the dark with lots of moving air around 65f and I have a dehumidifier set at 50%. I normally dry like this for 5 to 7 days, it depends on the size and density of the buds and that varies a lot strain to strain. then everything goes into paperbags or large plastic bags depending where in Europe the grow is. in the paper bags they are split into oz bags and its gone once its dry, there is no cure for anything retail, thats on the buyer. in the plastic bags its set into 1kg bags and sealed and opened every couple days for a couple weeks before its vac packed and shipped to its destination.
for flushing I tend to use only plain water. if they have had really heavy feeds then I may use something like you mention just to wash the extra salts out but normally around 7 days of water will do it for coco