On the topic of specializing cities, I feel that pure specialization is not too good at all. If you make a city completely commerce (cottages) it will have no food or production. Food and production are needed in EVERY city. Even if you don't want to make military units there, you'll still want building improvements or that city is worthless later on.
For this reason, I like to make sure I have enough food to work all the tiles in the later game. I like building cottages on grasslands since the 2 food supports the tile by itself. I also take into fact Biology, since almost all the time, you won't be able to work all 20 tiles in a city pre-Biology. So if I farma grassland, I look at it as 4 food instead of 3 later on, which can support 2 workers from just that one tile.
In regards to windmills, I like them almost always over mines. My typical rule of thumb is if a city needs food, use windmills, especially on grassland/hill tiles since it will increase food to 2. If the city has a good supply of food, I will use mines, especially on plains/hill or desert/hill tiles since it will be a pure production tile that can be supported by a high food tile. Windmills are like a "general" tile improvement, and gives a little bit of everything for those cities that are not lacking in anything. Maps like Highlands make really good use of Windmills because of the lack of food, and the high production rates from all the hills. Windmills on this map will hinder production by a tad and make up for the weak parts of the maps tiles in food/commerce.
For this reason, I like to make sure I have enough food to work all the tiles in the later game. I like building cottages on grasslands since the 2 food supports the tile by itself. I also take into fact Biology, since almost all the time, you won't be able to work all 20 tiles in a city pre-Biology. So if I farma grassland, I look at it as 4 food instead of 3 later on, which can support 2 workers from just that one tile.
In regards to windmills, I like them almost always over mines. My typical rule of thumb is if a city needs food, use windmills, especially on grassland/hill tiles since it will increase food to 2. If the city has a good supply of food, I will use mines, especially on plains/hill or desert/hill tiles since it will be a pure production tile that can be supported by a high food tile. Windmills are like a "general" tile improvement, and gives a little bit of everything for those cities that are not lacking in anything. Maps like Highlands make really good use of Windmills because of the lack of food, and the high production rates from all the hills. Windmills on this map will hinder production by a tad and make up for the weak parts of the maps tiles in food/commerce.