I might chime in here, as I happen to have played a litte with one of these really nice little machines, too.
Happy to share some takeaways, too:
- power consumption: 9W idle is the lowest I managed to get (proxmox/debian + powertop --auto-tune, just one SATA ssd). I doubt you can get any lower given that the iRMC draws about 4.5 W alone (if someone would find a way to switch it off, though...)
- CPUs: tested Pentium G4560, Xeon 1220 v6, and Pentium G4600 (which is not on the official compatibility list, marginally faster than the G4560, works fine)
- caddys: the previously mentioned STL file on thingiverse works sort of (3d-printed a few myself), at least for blind caddies. BUT: the screw holes are "on the wrong side" and not within the right distance from the backplane to let you connect hdds/ssds (at least for my TX1320 M3). Also there is a slightly thicker part on one of the side pieces, that does not really seem to go too well with the the TX1320 once you have screwed in a ssd or hdd. So I have been fiddling for a while with tinkercad (I'm no engineer!) to "fix" this in the STL file and ended up with something that's actually working well enough for my needs. Did not bother to upload the new file on thingiverse yet as the result is certainly far from perfect, but happy to share it here (check it out for yourself and only use at your own risk, of course!). Printing in PLA and PETG both works fine, could not test ABS (would be my preferred material due to highest ruggedness). Stiffness etc. is good enough in either material. Temperature should be no issue as you probably do not plan to let temps go up higher than 50 Celsius among the drives, I presume.
- orange blinking led: whenever you change CPU or RAM that's detected (hence the blinking led); to turn that off just go into BIOS (it will report the hardware change very briefly on screen, if I remember correctly), maybe saving (unchanged) BIOS settings is required too, to get rid of the blinking led (can't remember). After a new start the blinking led should be gone.
- 3.5" hdd: it's quite possible to fit in one in the big bay near the power supply. I had to very slightly bend the pretty stiff sheet metal guiding rail, though. And there are even two nicely fitting holes on the outer side of the cage to fix the drive with standard screws, which I found sufficient. No vibrational decoupling from the rest of the case, however.
It would be absolutely great to find some way to mount a second 3.5" hdd for a zfs mirror. But that seems almost impossible given the cramped space (without removing the 2.5 bays, of course).
Also, should someone find a simple way to elegantly improvise a 2x 3.5" cage for the space the 2.5" bays occupy (without having to purchase the OEM parts), I might consider getting a second machine. ;-)