About size. Assuming you take 0.5 meters for couch, display width will occupy ~22 degrees of your field of view. In my opinion, that is about as low as you want to go.
About angular resolution, assuming it's 1080p projector and content, you'll get ~85.5 pixels per degree [of your field of view]. That's not bad (you'd benefit with angular resolution up to ~200 pixels per degree) and you shouldn't worry about seeing pixel grid or any pixelation.