Installing & Configuring R9 380 PC without iGPU

Hello folks,

I have an old PC laying around with these specs;

Mobo: Asus P8P67 REV3.0

CPU: i5 2500

GPU: Sapphire Nitro R9 380 2GB

RAM: 2x4GB 1866MHz gSkill

I want to install Sierra on this configuration if possible. From my reseaches, my GPU will boot into a black screen if I don't use iGPU. Problem is that, I don't have option to use iGPU because my mobo doesn't supports it.

So even if I'll be able to boot up without using my GPU, how can I configure my system until that point?

As a last choice, I can buy a very cheap alternative OOB GPU aswell, but I would be very happy if I was able to use R9 380.

Thanks in advance...