Setting up a PXE boot environment - Part 0

Upon learning that Raspberry Pi 3 and above has PXE boot capabilities, I pulled out my dust gathering, poor Raspberry Pi 3B... My motive is NOT to re-image that MicroSD card every time I want to tinker stuff, simply plug-in, power up, and viola, at least ideally.

Following the guidelines from various sources:
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/net_tutorial.md  https://help.ubuntu.com/community/DisklessUbuntuHowto

Building stuff

When I was 12, a relative lend me a set of PC, I vaguely remember it was a Pentium 133, has a turbo button in its case, and a fairly large, 400MB hard drive. He lend it to me so I can take it apart and put it back, see if everything is still working.