yep I think you have most of it, but just looked back and noticed that you already have the boxing built for your fascias and soffits.
As before run all your tiles up the pitched roof with soakers and where you ask "what to do here" cut a piece of lead that covers the upstands on the soakers, following the pitch of the roof and then lap it up to underneath the bottom of the roof deck, no need to slot it through the deck.(right from the ridge so that it will begin under the ridge tile down about 2 or 3 soakers, make sure your soakers go right to the very top too) .
Then build your fascia and soffit box to cover it but leave it a couple of inches short of hitting the tiles on the pitched roof, again make sure that the pointy end of the fascia will end under the line of the ridge tiles. fit your fascia and soffits(closing off the end into the pitched roof will be tricky, but make sure you do or you will get all sorts of creatures nesting in your roof)
Then fit the edpm as you have drawn, you won't need a separate arris rail.
At the ridge, yes run the edpm over the top but just enough so it won't show once the ridge tiles are on.
I believe you are tile hanging the dormer cheeks, if so then obviously get those on before the fascia and soffit, which you may have to build down slightly to cover the nails.