Booting into legacy or UEFI from the live install USB is really quite simple.
When booting select the proper mode from the bios boot menu. It should show the USB twice, once with just the usb and once with a uefi overlay. If you select the one with uefi overlay it will boot into uefi mode and vice versa. The install will be performed in whichever mode you booted.
As far as the 2K or 4K screen, that depends on the GPU and drivers, not the boot mode.