i read that GOG has its own launcher or something, and im wondering if a new update releases will you be able to update?

The GoG release of Terraria has gotten all the updates released so far for the PC version.

You can use the GoG Galaxy client to automatically update when an update is available or you can go to the game page in your library to manually download a new patch. Historically GoG has been a bit slower (a couple of hours) to put up patches than Steam and they tend to prioritize the automatic patching via Galaxy. So if you don't want GoG Galaxy installed, you should expect a delay in getting the patch for the game, but it will arrive.