Your mention of the voting of liturgies on council members makes me think there might be another way to model the income of a trade city with little associated land governed by a council of merchants like the one you are describing. You could build it as a 1-hex domain with an urban settlement of whatever size fits historical estimates of its population. Then, you can determine how many total merchant ships are owned by members of the council, and the total number of people in the councilors’ families. Multiply the number of ships by the average monthly profits for a merchant ship (there’s a table with this info on ACKS pg 145), and the population of the councilors’ families by the monthly cost of the minimum acceptable standard of living for councilors. Subtract the second number from the first to determine the city’s available monthly liturgy pool. Calculate the domain revenue and expenses using the normal ACKS domain rules. Any excess expenses are taken from the liturgy pool. If it becomes important in the campaign, you can calculate the liturgy pool by family instead of as a total, or maybe do that for a handful of important families and then lump everyone else into a “minor councilors” pool.
The only big downside I see is that galleys aren’t included on the Merchant Ships and Caravans table, so you would have to figure out how to calculate average monthly income for trade galleys.
Still, this does give me a good model for a domain ruled by a Venturer and his guild.