I'm happy to see that Homeworld Remastered, which I bought on Steam, is now available to me on GOG through Connect. My question is, can I play the game "on" GOG with the mods that are available on Steam? And how would I do that?

Geoff

If you can download the mod from steam as files or installer, and that mod does not require anything steam related, then quite possibly. This is one of the big problems with steam is that, whilst not DRM, you are tied to their product and their services. Me, I like to not be tied to them, hence I use Moddb, Nexus Mods, and various other sites to get my mods, and I would recommend if your going away from Steam to do the same, and cut the umbilical.