It takes a long time to become a Rank 8 Sovereign with an equally esteemed city. Rural populations and new players flock to huge well established settlement. The first district you need to become Rank 8 is a Downtown. It's time to centralize your tall buildings and give the people a showy place to work and shop.
Building your Main Street (and starting the Downtown district) requires knowledge of Masonry. By the time you've reached Rank 8, it's very likely you've already got both Science and Masonry researched into a few levels, so this shouldn't be an issue. Players who go Downtown will be able to go on a Shopping Spree, risking a little currency for a chance at usable gear. The Main Street increases the tax income from all Commerce districts and processes Oil from fish. The Exclusive Office Building is built with Dyes and Paper and increases building storage Capacity for all buildings in the settlement. They also sell paper to Yeomen for Drachma. Mints are most efficient in the Downtown district but can be built anywhere. Your Downtown is likely to have high Prosperity but fairly low Security.
In order to build your Militia HQ, you'll need to do a level or two of Tactics research. Beyond this you need Iron Ingots and Leather for the actual construction and upkeep. This district is dedicated to training local troops. The Militia HQ trains Infantry units and reduces Canvas upkeep costs throughout the settlement. The exclusive Mustering Hall decreases training cost and increases training speed of Peasant Units. The Armorer building, your best avenue for crafting Armor, is most efficient in the Militia Compound but can be built anywhere.
A quick study of Astrology will allow you to build your Conservatory and start a Commercial District. Unsurprisingly this district belongs to the Department of Commerce. The Conservatory acts as an Income building, selling paper to Peers and players, and increases settlement Education. It also processes as a Weaver, leaving you a bonus source of Linen, Canvas or Wool. The exclusive Showroom takes a quick study of Aesthetics but increases Settlement Prosperity and currency income on top of selling any Good to Yeomen for Thalers. Weavers are most efficient in the Commercial District but can be built anywhere as long as you've researched Logic.
Another member of the Department of Commerce, if you like processing resources into goods, the Industrial District is for you. The main Industrial Park increase processing speed for building that is primarily a processing building. It also processes as Foundry, producing both Iron and Steel Ingots. The exclusive Factory increases all processing speed in the settlement and itself processes as a Weaver. Each Factory also increases Prosperity and decreases Health in every district. Tanners, which produce Furs and Leather, are most efficient in the Industrial District but can be built anywhere.
The Leisure district is a great way to extract currency from your NPC populace. Both the main and exclusive buildings sell several things to your population. In order to build your Casino and found the Leisure District, you must first do a little research on Statistics. Without it, your Casino would not be resilient and would lose money rather than making it for you. This temple of gambling sells Beer to Yeomen, Wine to Peers and Bread to Peasants while they play their games. The exclusive Dancehall sells a lot of Beer to Peasants and Yeomen while they work up a thirst kicking up their heels. This building also processes Beer and increases local Health because dancing is good for you. Breweries are most efficient in the Leisure District but can be built anywhere.