If you're willing to edit the raws you can butcher goblins (and any other sapient Which is a fancy word for humanoid
creatures) it can and has been done.
Just change [ETHIC:EAT_SAPIENT_OTHER:UNTHINKABLE]
[ETHIC:EAT_SAPIENT_KILL:UNTHINKABLE]
[ETHIC:MAKE_TROPHY_SAPIENT:SHUN]
to
[ETHIC:EAT_SAPIENT_OTHER:ACCEPTABLE]
[ETHIC:EAT_SAPIENT_KILL:ACCEPTABLE]
[ETHIC:MAKE_TROPHY_SAPIENT:ACCEPTABLE]
This has the side effect of you being able to also butcher humans, elves, and any other sapient (humanoid) creatures.
Does this work now? I could be crazy, but I thought in previous versions you still couldn't butcher sapients even if the raws were modded as described. I thought it used to be hard coded as impossible, even if ethics were changed such that it should be possible.
But you definitely CAN butcher them now in adventure mode (which was previously impossible unless you were starving), so maybe this has changed? Have you actually succeeded in butchering humanoids in fortress mode?
For OP - if you set up a fishing industry and you have a river, I don't think you should have much trouble getting enough food. But maybe you don't want to include fishing as "hunter/gatherer"?
If you want to make it easier, you could start in summer or autumn, so that there are more plants to gather. With the new plants there are VERY large amounts of food that can be gathered in most biomes, but only once the fruits appear in summer/autumn (gathering before then just removes the plant).
If you aren't finding enough animals on the surface, you could go hunting down in the caverns. You probably would want to have your military kill the things you find down there and then butcher them afterwards, rather than just assigning dwarves to hunt, as a lone hunter may not be able to handle many things in the caverns.