With the 4-lane OcuLink through dual M.2 board, I need to follow the right power sequence for the card to be recognized in Windows. I also remember fiddling with error43 fixer a bit to get it working.
I would recommend you get the dual M.2 board and some M.2 to OcuLink 4i adapter (this is an illustration of a nice solution), get the GPU going through that and then move to your own solution. This way you eliminate software preparation as a factor for issues.