I'm starting from ground zero, so this board is my first S100 component. That means I don't have a backplane / power supply to plug it in to (that's my next project), and I don't have any kind of system monitor / front panel to interact with it.
Fortunately, John's instructions don't entirely assume those are available to you. Still, I did have to go pretty far before learning I didn't make any early mistakes.
I decided to power the board directly with 5V, plugged into headers soldered in where the Pololu regulator will eventually go. With that, I was able to verify the first few liveness checks using assembly code burned to EPROM (also a first for me - the cheap-o knockoff programmer worked great).
Here's a photo of my first major milestone: the system monitor prompt.