Zephilia

Okay thank you so much again! Will download the driver from AMD.

There will be no problems if you keep the iGPU enabled.
 
I would get the drivers from AMD, personally.

@Crunchy Dragon In the end, I got the RX 580 Sapphire Pulse 4GB because it was the only available by the time I was gonna order, the 8GB was sold out >.<. It'll be shipped tomorrow. So, currently my rig is powered by the iGPU (Intel HD 530). And here is my question, if I installed the GPU and connect it to my monitor, will the iGPU be disabled automatically or do I still need to disable in the BIOS? And so all I need are the drivers for the GPU to work properly. Thank you so much.

RX 580 is the best price/performance card currently, unless you factor in used 1070s, 1080s, and 1080TIs on Ebay.
 
If you're buying new, I would go for the RX 580 8GB.

The extra 4GB will last longer as games get more demanding.

I see. Thank you so much for the enlightenment.