It has only just occurred to me how 'small' the Anachronism need be...
Firstly, let us take the guild's 'population' to be 1250 (i.e. the no. of members) ~ assuming it is only 'us' which populate the guild-city.
Now, two comparisons can be made.
If we take the Anachronism to be a city-like layout...Taking London's average population density (being a mixture of small & large accommodations) of 4,761 / km². The Anachronism need only be 0.26 km² (510x510 meters) [or 1670 x 1670 feet] in size (not particularly large at all) if it were a real city. This is assuming, as well, the city only has one deck/tier.
This corresponds to a mere 1/350th the size of Manhattan island.
Of course, one might wish to increase this to take into account the various City-residents who are not represented by Gaia's members; and more space for extra docks and the like; but the size is still not very great.Or, if you'd prefer to see the Anachronism as a giant Airship or Boat...Taking
MS Majesty of the Seas as an 'example' cruise ship; it is 268m/880ft long and yet holds a 'population' of 3500 people.
Such a sized vessel would therefore make a very decent home for 1250 people; adapting it for longer voyages, of course.
~
Naturally, if the Anachronism were to be considered both a ship
and a city, a mixture of these two comparisons would be required.