10 ply = aran. = 5mm needles.
I am a very experienced knitter over 2 decades of intricate knitting of many many different combos. As a quick browse through either my gallery here - or at ravelry (happiclown) will show you. I am/have been a commission knitter for companies that sell garments internationally I also write and alter patterns-
all false modesty aside I have done patterns in a foreign language with less
if Natnz and I are struggling I would seriously consider a rewrite of your pattern. I wont touch your short rows explanation

