You already have a windows machine running. It's easy then.
Option A: You need a USB box for the HDD. SATA may work, too. But I have not tried it yet. (I have a native Windows PC)
1) Boot to Window 7 (on your 5,1):
- Download Windows 10 ISO. Need to be an old build (mine is build 1803 and worked perfectly, newer build may fail the WindowsToGo style)
- Download and install Rufus (
https://rufus.ie/)
- Download BootCamp 6 (
https://mega.nz/file/7E0l1LxI#Y41IkRECUEZ-PrduAdjosJoOSA9bojWXj1O5Rv8AEdg)
- Use Rufus to write the windows ISO to a blank SSD (
NTFS format, MBR) on the form of
WindowsToGo. I have not tried the HDD connected to a SATA cable yet. I installed it via a USB box.
- Copy BootCamp6 files to a folder on the SSD you just installed Windows 10.
- Eject (unmount) the USB box. Take out the SSD
- Insert the second SSD to the USB box, plug it in the machine.
- Run Rufus again to make the second SSD.
- Reboot to OSX.
- Turn-off the MP and insert the SSD back to 1 SATA slot on MP 5,1.
2) Power on the MP again:
- It will boot to OSX as normal
- Open System Preferences and open Start Up Disk. You should be able to select the Windows 10 SSD as start up disk by now.
- Boot from that SSD to Windows 10 and continue to install drivers.
- You will need to install Boot Camp to Windows anyway because it will automate the driver installation process, plus help you boot back to Mac OS from Windows desktop.
After confirming that the new WIndows 10 SSD is working fine. You can migrate data from windows 7 SSD and delete it afterward.
Option B: You need 1 USB (thumb drive or SSD in USB box, doesn't matter)
- Boot to Windows 7 on your 5,1
- Download the windows ISO, but choose the option: Make USB installer.
- When finished, eject the USB installer
- Plug it in again, run setup.exe if it doesn't run automatically.
- It will upgrade your windows 7 to windows 10.
- Now clone the windows 10 SSD to the second SSD.