Call to research: difficulty levels affect building costs - what else?

I saw a post on another forum and could not believe my eyes. So I went and did a quick test. The person was right - playing on hard artificially inflates building costs by a significant proportion. Hundreds of koku per building.

So now I'm wondering:
1. What else changes across difficulty levels in order to provide artificial challenge. Happiness? Research speeds? Unit costs? There's a whole can of worms here.
2. What the percentage increase is on each difficulty level.
3. How much worse it gets at very hard and legendary.
4. Does easy get a cost reduction?

Anyone care to help research this? I'm not great with statistics.

Here's some preliminary figures:

Large town: E - 2450, N - 2975, H - 3500
Fort: E - 2700, N - 3375, H - 4050
Tenant fields: E - 2380, N - 2890, H - 3400

Hard, very hard, and legendary all share the same costs. As you can see, between easy and hard there's a huge difference in costs. Over 1,000 koku per building.

Unit recruitment costs are different too. I've only got limited figures so far. Levy spears are 406 on normal, and 435 on hard.

I assume the AI factions aren't affected by this.

hmm strange indeed.

For Large Town and Tenant fields it's:

70% - 85% - 100%

whereas the fort has

100% - 125% - 150%

For the last few years, everytime I decide to start a S2TW game, I see a new huge imbalanced advantage an AI has and I quit the game in shock. Diplomacy, unit scales, attack priorities..

Last time, I see the AI gets extra free units to their attacking stacks out of nowhere and I was shocked. Yet there is still a new one comes up.

Anyway at least this one looks like they are not overpricing on legendary, they just lower the costs on easy mode.