Unibeast does not recognise GUID USB, just MBR

Hi!

I'm trying to get Unibeast to prepare a USB drive to install Sierra on my PC. However, it actually fails before I can do anything as it does not recognise my GUID formatted drive. When using MBR the drive is recognised just fine but I can't actually enter the bootloader. From what I gathered, this is impossible (or at least accompanied by a few work-arounds). If I let Unibeast do its thing with the MBR drive it will succeed in doing so but when I try to choose the drive in order to boot from it it will a) not be listed as UEFI and b) will skip it directly and boot straight into windows. Are these problems connected or two distinct topics?

I read that Unibeast sometimes struggles with 8GB USB drives just as I am trying to use. Is there a quick way to fix that?

I want to install Mac on my PC on a separate drive and my PC is UEFI capable, my Windows (on a different drive) is however Legacy based. Is this a problem? From what I understand it might become troublesome when I try to install them alongside on the same drive but shouldn't be a problem when using two separate drives, right?

Thanks!