Having a horrible/fun time trying to play the Aizu has taught me a lot of things:

1. Castle upgrades are great for defense AND repression, especially compared to buying (or being stuck stationing) troops for extended periods of time.

And they don't hurt you economically like they do in Shogun 2, besides the fact that they cost money up front but they do tend to work forever afterwards to DEFEND your other investments.

Police stations are basically JUST for repression (and the agents), so I tend to install them everywhere only after inns and cottage industries start becoming a happiness problem.

2. Waiting for an enemy to finish an expensive upgrade that you want (like especially when they're one turn away from upgrading their settlement) saves you the cash AND the time it'd take to do it yourself.

3. Draining your neighbors of cash by selling them military access early in the game WILL make them weaker and slower (and give you a jumpstart on your own economy) but that could be bad or good for you depending on what is going on with the clans around them and what they would've normally done (to you or for you) if you didn't drain them a bit.

Its basically free money aside from that, though, since its so easy to get the AI to attack you by "boxing them in" when they're all programmed to expand at all costs.

4. Ships cost a lot of cash to keep running every turn, so try to avoid Huge Navy Stuff (if you can) until you are richer.

5. Learning the natural tendencies of your neighboring clans for growth and avoiding "the head of their snake" can save you cash by not making you fight battles on more than one front at once and you can start using that knowledge to your advantage (taking weakly defended or war-ravaged places with the minimum size army necessary to do it efficiently, letting them block or weaken your enemies for you, etc).

That's actually very economic heh.

5. A 2% bump from a settlement upgrade (plus more economic buildings) is a big deal per turn when you are taxing folks at the minimum rate of 10% to improve growth, and not something you'd feel so much if you were used to a 30% tax rate.

6. Entertaining noble geisha are great for cranking up the cash on a province and your police agents can get bonuses to repression (saves you time and money with newly aquired properties by not having to station troops).

7. There's a lot of ridiculously good tech tree upgrades for your economy.

8. Farms are good, fertile farms are great, very fertile farms are unfair haha.