What do we know about the economy?

[Rothe]

But a single market gives you +5 to that provinces growth and the ability to recruit metsuke and the upgraded castle gives you better spawned defense troops, very tiny bonus to bushido arts and at higher levels they also increase replenishment rate. Therefore you should avoid upgrading castles just to include market once you reach the maximum number of metsuke.

Actually, my tactic is to find provinces where I am not going to do anything else (like recruitment) and reserve them for markets. That means, I would not upgrade a military town castle to include a market in any case. I am better off conquering a town and putting the market there (even scrapping an unneeded troop building).

It might actually be better to recruit your metsuke from philosophical tradition province. If you're only ever going to use metsuke to oversee town you don't need +2 experience levels. To max metsuke efficiency you'd need top level market in a philosophical tradition province.

I agree. Although, doesn't the extra XP mean extra tax in any case, or is there a limit to what a Metsuke can add?

When ever you have trade commodity, it's spread evenly to your trading partners. Evenly here is relative, it depends on the size of clans. Big clan buys more silk than a small clan. Any surplus that you can't sell to trading partners is sold within your clan automatically for a smaller price.

So, basically it just means it is better to get enough trade partners to avoid surplus. I am guessing that it is always better to have more partners.

I still am a bit at odds with the value of a trade route shown on a sea lane to a trade node, and how that gets converted into profit for me. For instance, after the realm divide I am without any allies, but the sea lane values are still the same, even if I should now be using the goods for my own consumption (which would mean they have less value). But I am guessing the value of the outside trade to the nodes is separate from the value of trade goods I get from there.

Edit: And yes, metsuke give 5% bonus to taxes per level (character effect part) which is of course then reduced by your administration cost.
If you see any number not divisible by 5 in character effect, this is because you have a general as finance commissioner.