It would be a good idea to go to Nexus nods asap and download the Unofficial Fallout 4 Patch (UFO4P) version 2.1.5 before it disappears. This is the only version which will work with GOG Fallout 4 version 1.10.163 (“OldGen”) - and the mod author clearly states that it will be removed as soon as the GOG version of Fallout 4 gets updated, which could be any time now.
The latest version of UFO4P (2.1.6d) will not work with ANY version of GOG Fallout 4, either “OldGen” or “NewGen” (if and when it arrives here). That mod’s author has stated clearly that if the GOG version differs from the Steam version - and GOG has at this point confirmed that this WILL be the case (i.e. no CC content) - then UFO4P will not make a special version for GOG. In other words, “NewGen” GOG Fallout 4 will never work with the Unofficial Patch or any of the mods which depend on UFO4P as a requirement.
I would download UFO4P even before buying and backing up GOG Fallout 4 version 1.10.163 since I’m pretty confident that GOG will keep the “OldGen”version available for download even after the “NewGen” update arrives, hopefully permanently because the “NewGen” version is going to be crippled for modding. Still, definitely best to download this and back it up in good time.
It’s a good idea to grab F4SE build 0.6.23 as well, although you can always get older, archived versions of F4SE from silverlock at any time. I’ve no idea why the same isn’t true for the Unofficial Patch, I just cannot understand why the UFO4P author(s) feel it necessary to remove all versions except the current one, especially in cases like this.
TL ; DR :
1.Get Unofficial Patch version 2.1.5 (under Old Files) from Nexus. URGENT.
2. Download and back up GOG Fallout 4 version 1.10.163. SEMI-URGENT.
3. Get F4SE build 0.6.23 from Silverlock. NOT REALLY URGENT.
4. Download any mods which require UFO4P. I’m afraid I don’t have a list of these. SEMI-URGENT.