After some trial and mostly error, I've come to seek help. This is my setup:
Dell Inspiron 5759
8 GB RAM
Internal GPU: AMD R5 M335
EXP GDC v8 via NGFF (wifi card)
External GPU: AMD RX560 4GB
What I've done so far: I first started with a GTX 1050Ti. My laptop did recognise that card, but obviously I got the code 43 error due to NVidia banning the use of eGPU's in their 10xx series. So I returned that card and bought a RX 560 instead. But now I have even more problems. It's either blackscreen or booting on the internal display. I've tried to hotplug (boot with wifi card, and then when in sleepmode swapping for eGPU), delay the boot by going into BIOS, turning the ATX power on (permanent power via EXP GDC). The only thing I haven't tried is the delay on the EXP GDC.
Any help is greatly appreciated.