HP thin client
I expect it to work; make sure you compile with optimalizations (-O2 or -O3), and it will perform nicely on older / less-capable CPUs (I'll update docs on how to do it).

Note: you can run the whole stack on a single windows laptop, the rbpi/minipc is a nice-to-have.

Active SDR loop amp or 1:9 balun
I'd prefer the active solution; the antenna *might* pick up disturbances (ie. sparking of motor commutation), and having an active device provides some additional safety. I haven't had issues with the 1:9 baluns neither so far (note though, I'm using the "clifford version" hackrfs, which have additional frontend protections).

Timing software
You can download ZRound Suite without admin approval or registration.
NextLevelTiming: unfortunately (last time I checked) it supports only serial port / usb based decoders, the TCP-based ZRound protocol is not supported.

Programming JIG for transponders:
Any contribution is welcome, and a programming JIG is a nice idea. If you share yours, I'll to link to it from project readme; or send a PR to the project having the files inside.

For now, I use pogo pins soldered to 2 mm pitch row header glued together.