Yeah, I can't really tell how that comes apart. Some devices you just run your fingernail around and others you need a hammer (not really). The Nook Glow2 is put together with special double stick tape and you'd better have a supply if you want it to go back as it was. Is the back shell on the Leaf seamless and the only crack is on the front *inside* the outer shell? I've not seen one with screws like that. Any chance now that the screws are gone that holding it face-down and giving it a gentle whack that that bottom edge drops out of the shell? I think that it's more likely that this is stuck together with tape and the two screws are just to keep the Type C connector more secure, since you'd actually need clearance to pull that bottom edge out.
On the Glow I worked around the edges with a single edge razor blade. When I was through I cleaned up the old tape and used some new double stick (special) Tesa. I'd hate to see you mess up your new device.
https://www.microcenter.com/product/...tape-4-mm-wide
900E is the DIAG interface for Qualcomm devices. It's much less powerful than the 9008 actual EDL interface. I guess there might be a way to switch modes, but I have no experience of that. You might try with some more button acrobatics to see if you can get 9008. 900E is like a serial port and should/will appear under Device Manager there.
The 9008 is different. I'm running it with a generic driver. "Zadig" is a generic WinUSB driver. Just google it.
Edit: Are you sure that your Fastboot is broken. That usually doesn't happen, it's more likely that you have no driver for it. Google minimal fastboot.