I always love these cool cyberdeck style builds but whenever the bug to build my own catches me, I end up realizing i'm just trying to build a really bad notebook.
I've bought a few old Chromebooks off of eBay recently (for around $20 USD each), and re-flashed the BIOS so that I could install Debian on them.
The student-oriented Chromebooks are reasonably sturdy, and at that price point, I just don't care if something bad happens to it.
TTL-level serial port pins exist as well.
Then optionally you can connect your motherboards power/reset pins so you can reboot or turn off remotely.
Video is a third party HDMI capture card that plugs into the Pis camera port.