I can confirm your point b., I’ve done exactly this case last week.
1) I installed a brand new ZS3.2.x box, without changing *any* default setting.
2) from b16 I exported the configuration (both without and with logs!) by the GUI (quite long, I had a 8GB compressed file from a 36GB profile)
3) I uploaded the configuration exported from b16 on the new box using the new-box’ GUI.
4) I moved the network cables from the b16 and turned to the 3.2.x box (just looked at the correct WAN/LAN ports from ZS command shell)
5) et voilà, everything was simply ok.
So, I need help on your point a.: “[how to inbox] upgrade from 1.* to 3.*”?