Removing that much timber could cause your plasterboard to warp and the plaster to split over time, especially as it'll be experiencing significant temperature changes. I would expect, however, that you'll need to create some kind of frame to attach the fire to.
You should concern yourself with the potential for fire risk as well, and therefore the required clearances for the fire from such combustible materials as the timber frame and the plasterboard. Some parts of the fire will undoubtedly get very hot during use