I think one of the biggest things I've learnt from this project is that manufacturing (more than one-offs) things which aren't just straight PCBs is really hard, despite having some R&D experience in many of these aspects. It's also been surprising how long seemingly trivial tasks take. I had a bunch of estimates on how long various tasks would take for each probe. Pin assembly, testing, customs paperwork, etc. For almost everything I've underestimated the time requirements, despite having some experience in all of these things in the past.
I have been thinking on ways to improve my workflow for subsequent batches, including test jigs, and assembly jigs for the pins. It's definitely tricky as these kinds of tooling jobs take time to set up, and the time-saving payoff will take a while to reach.