The moss is artificially introduced. I grow indoors in a grow tent, with a misting system. So there really isn't an opportunity for the moss to establish naturally. Once I put it there though, it grows quite well. I find that if the moss is happy and growing, then the roth roots seem to be quite happy as well. I have a moss cap on almost all of my paphs, the plants really seem to love it (some moreso than others, but I have only seen a couple that actively seem to dislike it).
I don't do oyster shells, but I do add dolomite lime periodically to most of my paphs and they seem to really like it (roth included) so I would imagine that the oyster shells would be good. Mine grows under pretty high light conditions (I haven't exactly measured, but I would say cattleya levels or very close). I have a 300W LED grow light (red,blue, white with UV/IR) which I keep about 2.5-3 feet from the plants. It covers about half of the grow tent (creating 2 light zones). Strap leaf paphs like my roth grow right under or just off to the side of the light. Mottle-leaf guys grow on the other side of the tent and receive less direct light.
To clarify my exact watering regime, I also supplement Mg, since I find that what is in the fert doesn't seem to be sufficient, but I was wary about increasing fert dosage and overdosing other stuff. So, I use RO water that starts at 10-20 ppm most of the year, I add about 1/8 tsp/gal of epsom salt, MSU RO fert at 30 ppm N, and about 5-10 drops/gal of Superthrive (which has concentrated kelp extract and other stuff).
I wish you the best of luck! Hope it grows nicely for you.