It really depends on how dedicated you are to the 100% completion goal. A lot of players will consider their farm complete when they have completed the community center, seen all of the endgame content, and the game runs out of steam. However, other players will not consider their farm complete until their farm has all the magical buildings, is fully automated, and looks pristine. As I said, it's down to your overall engagement and how motivated you are to perfect your farm.