(1) PixInsight's servers are heavily loaded, and the first time I downloaded it, I got a seemingly normal .exe file that was actually incomplete. The symptom was that, when launched, it ran for a few seconds with nothing on the screen and then stopped.
Check the published checksums. Or check the exact length, 292,345,896 bytes for the Windows 64-bit version.
(1.5) You have to uninstall the previous PixInsight in order to install the new one. However, the previous one can still be downloaded.
(2) Per the release notes, the license file has to be regenerated and is stored in a different place (in Windows, it's somewhere under %appdata%). As I understand it, the regeneration can only be done once, but the license file can be copied to multiple computers as long as you put it in the right place (which is not the same as for earlier versions).
(3) The PixInsight FAQ assures us the license terms are the same as they have been -- per-user, not per-computer. One individual can install and run PixInsight on any number of computers. (I didn't see anything about not running it on more than one computer at the same time, provided one person is doing it! And that might actually be practical when doing a big processing run.)
I am just doing the upgrade now. If it doesn't go as expected, I'll be back with notes.
Edited by Michael Covington, 17 December 2018 - 10:56 AM.