I have USB 3.0 ports available. Can I run a external USB 3.0 as my main HDD?
can, but install on external usb disk will be not easy. depending on the motherboard if can detect the external HDD when installing the windows.
And you have to keep on plugin the external HDD on the same port once you successful installed the windows. The usb HDD cannot plugin to other usb port and PC to boot up. Whole Data cannot be loaded and readable on the other device if you are formate the system to NTFS.
so, think about it before you install the windows to external HDD