I don't know if there is a company workshop bonus that comes from larger houses (I suspect not, but someone who knows better could correct me). The main perks of a larger house are more decorating space and an additional garden, so more plots for crossbreeding. If you're leveling crafts, you can also put more crafting stations in a larger house. That's about it, though. For a FC that small, I think a small house would do just fine, and you could always save up and upgrade to a medium later on if you find you want more room.