waltc: Installation failed for me, too, initially. So I uninstalled the game through Galaxy and am now reinstalling the whole game @129.16 GBs, according to the Galaxy installer. Patch 7 was supposed to weigh in at 11.66 GBs, but as I say, that install failed in Galaxy. Hence the complete reinstall. When that finishes in a couple of hours, I'll report back in this thread with the result.
EDIT: OK, the reinstall worked fine, and the MOD Manager is included in the GOG update. BTW, the GOG update--at least the one I downloaded--said not a word about Patch 7. But if you see the Mod Manager button on the Main Menu--you have patch 7.
Did you get an 11.66GB update from Galaxy? Mine just started downloading 124.61GB, which is about the size of the full installer. I almost decided to wait and see if the offline patch would be smaller, but decided to let it go. I wish I'd thought about it sooner, but I should have just grabbed the full offline installer, but I'm already 60% on the "update."