What Order to Build Things in to Properly Construct an Economy - Trade Opportunity and Trade Potential

The title generally says it all: what order do you want to construct buildings in in order to maximize your economy's potential? When is it appropriate to interrupt my economic growth to construct military buildings?

By the way, I apologize for the incredibly long period of no posts - I didn't realize that this became the top hit for MOS strategy style searches, and figured nobody was reading them. The guide will now be regularly updated. If you have questions on how to do something, are stuck in a jam or are getting overrun, or even if you need help winning a battle, leave me a comment and I will see what I can do.

Details end up being quite country specific (especially decisions on when to construct military buildings), but I can use my understandings of the mechanisms to give a general plan. If you have been following me, you know that I mean relatively general - my analyses are always very complete.

If you are not building a diplomat at the start of the game and trading around map information and trade rights with everyone, you're playing the game wrong. All of my guides assume that you are playing the game right in that regard.

First, a discussion on theory. Farm buildings provide increased crops, both for selling AND for population growth at the same time. Markets and fairgrounds and the other stuff in that tech tree, where what they do is "Increase amount of trade-able goods" increase your Trade Potential. This is how much you can sell if you have unlimited Trade Opportunity. Think of it as your factories. This is how much stuff you actually create that can be exported. Keep in mind that the net increase in trade from these buildings is more than is shown in the city statistics window, as it will also have an impact on the trade in your other cities (how much depends on road/shipyard status and distance). Population matters significantly in Trade Potential. Although more population will decrease the amount of food that can be sold, it will increase the number of people you have working on the farms and producing products for trade. In general, increasing population results in increasing trade income and increased tax income.
Roads, Merchant Wharves, Shipyards ect... improve your Trade Opportunity. This is how much trade can actually take place. Think of it like as how easy (and thus how encouraging or discouraging of trade) it is for merchants to get to and from your cities, and how fast can then buy and sell goods, and then leave to go home and restart the journey. Keep in mind that the net increase in trade from these buildings is more than is shown in the city statistics window, as it will also have an impact on the trade in your other cities (how much depends on Trade Opportunity statuses). Population matters little to Trade Opportunity.

These ideas combine to decide how much trade you will effectively get. In order to do ANYTHING with Trade Potential, you need Trade Opportunity. (Though due to balancing, an increase in Potential after you have exceeded your Opportunity will increase trade revenue very, very slightly [often taking 100 turns or more to pay for itself]). You cannot sell your goods if there is nobody to buy them.

Increasing your Trade Opportunity once it exceeds your Trade Potential will still provide increases to trade, because foreign merchants might sell something to local merchants who then sell the item to a different foreign merchant for even more money, or foreign merchants selling to one another and you taxing the exchange. The increase in funding will be minimal, although roads will still provide vastly increased movement and Trade Opportunity.

 (Roads provide diminishing returns to both trade and movement. Dirt roads are far better than traveling in the wilderness, but gravel roads are not that much better than dirt roads, for example.) Dirt roads provide the largest bonus over what was previously there. Gravel roads provide a smaller additional bonus than the dirt roads did but it stacks with the dirt roads, and paved roads add more bonus than the gravel but less than the dirt roads, and they stack with both the dirt roads and the gravel roads. Thus, the dirt roads, also being the cheapest, are by far the biggest bang for your buck, although the increase in trade, if you have extra Trade Potential so that you can make use of the extra Trade Opportunity, will quickly pay for itself.

Ideally, you will try to balance your Trade Opportunity and your Trade Potential. Remember, a province with roads  surrounded by areas with no roads will provide vastly inferior improvement compared to a network of roads connecting to another nation. Build your roads accordingly, to ensure that roads bring merchants into your country.  You can gain an idea of your Opportunity/Potential balance by flipping around your nation checking the relative income increases from Potential buildings and Opportunity buildings.

Of course, you should absolutely prioritize farming buildings and other population increasing structures. As population is a percentage growth, the earlier you start it, the bigger and faster it will grow.
Generally, it is best to build road networks first (secondary priority to population increasing buildings, of course). Make sure you connect as many provinces as possible with dirt roads before you go around spending money on gravel roads and paved roads - you could build 2 or 3 dirt roads for the price of one paved road, and the dirt roads would give you 5 times the benefit plus the benefit of connecting your provinces. After that, you should go for Trade Potential buildings in your largest cities, and (as a secondary priority to the Potential buildings) shipyards/wharves in your coastal cities.  Finally, start on the advanced roads in your biggest cities. Finally, you can start on Potential buildings in your smaller cities. If you really want to, now you can put the advanced roads into your small cities, but by this point, your military capability is seriously behind, and you should start building the military buildings in your larger cities.

I'll probably come back and add more to this post. If this wasn't comprehensive enough on the build orders, come back in a day or two.
EDIT: Yeah, I think I'm done with this post. If you want a guide on economic buildup for a specific faction, let me know, and I will make it.
-Sapoman