Group synthesis (That thing teased ever since 1.0 to build ships and giant cakes and other grand projects) isn't even out yet. Even if there was a housing size requirement for a worskhop, I don't believe houses have workshops yet. That all said, I highly doubt they're going to put out that content they've been teasing for fricken forever, and then restrict it in such a way that only the smallest fraction of the population can use it ever.