Well, I think I’m complete on the build. A few more pics to follow up my original post above:
My wobbly crown was indeed due to the pen being very loosely attached - once I secured the pen holder it came out much better (and I probably should have made the pen itself even tighter):
I posted some notes on the Jackpot board and homing in this thread - Doug’s video was very helpful: VIDEO: Tramming & Squaring with Jackpot controller (LowRider v3 CNC but possibly helpful with MPCNC and others as well) - #14 by Hillsdale
Cutting the struts went mostly ok, once I figured out ESTLCAM and where to put tabs, etc. I lost the first one halfway through - my 1/4" plywood sheet wasn’t screwed down tightly enough (and closely enough to the cut) and pulled up a bit, enough that it wound up cutting through the tabs and the piece came loose. Put a bunch of screws on either side of the next strut cutline and after that it worked really well. I put them back into place for this photo. (The fourth one there started off a bit haywire with that scratch so I aborted right away.)
Here’s the front and back of the finished build:
I’d say about 3 full days of effort, starting with the hardware kit and pre-printed parts from V1E. Most of that time was also spent binge watching Community while assembling, so YMMV.
Now to figure out what to make… 
Thanks again!