You do not need to make a new farm... unless you want to play around with those new options that can only be set at game/farmer creation. Examples include setting the "guarantee 1-year completion possible" for the CC, remixing the CC, remixing the mine rewards and playing on a new map as you already mentioned. There are some cut scenes that you can only get early game, but they don't add anything but flavor. All the late-game stuff should be available. Tip: you'll have to load the game and play at least a day before you'll start getting any prompts for the new content.
