Some changes to my desk design:

In no particular order:

I rebuilt about 90% of the model so that it's driven off of an Excel spreadsheet. It took a little while, but makes updating tubing diameters *so* much faster.
The tabletop and shelf are designed to be phenolic resin; the shelf doubles as a footrest. I'm a bit worried that the long span on the tabletop will result in bounce, but that'll be relatively easy to fix if it happens.
The frame tubes are filament wound carbon fiber throughout.
The lugs/brackets are all slotted; they'll be printed. The band clamps are a little bulky for my taste, but the practicality of making the frame modular is just too appealing to me. Plus, I'm pretty sure they'll distribute the clamp force evenly and be plenty strong to hold the frame together.
My current plan is to drill and countersink the tabletop and then use flat head screws with washers & nuts to fasten the leg brackets.
The legs are angled, and I'm planning to use swivel mount feet with rubber pads on them. I'll install nuts in the bottom of the legs (method TBD) to hold the feet in place.
Having dummy models to serve as Utah teapots is *really* nice. I'm still missing my Wilton vise, Gerstner tool chest, and monitor/laptop stand, but none of those is worth the time it'll take to model them.

I'm pretty happy with this so far - hoping to have it together soon :)