Unimportant Food

I will take a crack at it.

When you choose a 7 food plot, it makes the final city size 40% bigger. But you usually have a 3 plot of another basic resource. Troop sov consumes all basic resources evenly, so eventually that 3 plot limits the final sov the city can support without going negative in that resource. A 5/5/5/5/5 plot gives equal amounts of all basics, and removes that limitation, allowing for considerably more production sov to be claimed. Since the city is 40% smaller, the gold production is 40% smaller, too, and the final army size would be smaller. But your replacement speed would be very fast, up to 5/3 faster.

It is an interesting theory, but probably not very useful in practice. You will likely never hit 10 cities using 5 food towns. Also, some buildings like infantry quarters consume basics, which would cut into basics for sov. Finally, you probably wouldn't be able to use all the main production buildings, which would limit your items (but I haven't run the math on that).

I think it would be easier to just buy or ship in basics, and run negative on the 3 plot resource during tournaments.

The 7 food cities to which I referred were the typical 5/5/5/3/7. That configuration probably represents 80% of Elgea, minimum. Most such cities will have +150% to +200% troop sov when they are building troops for a tournament. Some players temporarily drive that higher by going negative in research points, or cutting taxes and suffering a large gold deficit, or both.

The "least necessary resource" for choosing the 3 is whatever resource your military buildings don't use. Infantry quarters use stone and iron, so it would be a 3 wood or 3 clay city. Cavalry parade grounds use wood and clay, so they would be a 3 iron or 3 stone city.

I don't know what's inside a 5/5/5/5/5 city. You'd have to ask someone who uses them (if anyone). I would be curious if they have military or diplomacy buildings inside, as those would ruin the symmetry of the 5 resource plots.

Even after you have 10 cities, a 7-food city will allow you to run a higher tax rate to maintain a larger army.  So again the major consideration is whether you are going to maintain a large army in the long term or consistently be losing troops and wanting to replace them fast.

5 equal offers by far the most flexibility.

Tamaeon, if you are building a 5 food city to maximize sov structures, why would troop sov be the last thing you consider?

When you use the 5 food approach, do you still use infantry quarters and other upkeep discount buildings? Doesn't having 2 or 3 really cut into the possible sov? What tax rate do you set? I had been assuming 0% or otherwise very low.