1. So would you say that stainless steal is the best?
- Yes, one of the best. Also try Third Age Total War if you're a Lord of the Rings fan.

2. Does it update the scenarios or just the big European campaign (by scenarios I mean 4 campaigns that came with kingdoms: Crusades, Teutonic, etc)?
- It's an independent (mod foldered) modification that vastly improves the big European scenario. It does not disallow you to also play regular Medieval 2 or the Kingdoms campaigns.

3. Are you using steam and if so did you need to do anything to resolve any conflicts betwe
en the mod and steam?
- I myself am not using steam for M2TW in particular. However, there are some things that you need to take into consideration when installing for the steam version. Here is a list of great mods for M2TW with Kingdoms installed. Here is the SS thread for downloading it. Here is the FAQ, steam installation included.

Also, a few more non-mod related questions:

4. I noticed that if an army of raiders (or bandits, I forgot the actual term) is on your territory and they are not wiped out within a turn or two, the land where it stands appears burnt. Even after the raiders are wiped out, the burn mark remains. Is this strictly appearance or does this represent a permanent reduction in the economic productivity of the province?
- It's called devastation. Usually it will go away, but there is an annoying bug in M2TW that makes it permanent. Sadly the only way to avoid it is to curbstomp them asap. Also, they're called rebels (legacy of Rome Total War)

5. I wanted to sort out an economic policy more intelligent than More People + More Economic Buildings = Good, which is a true statement but isn't specific enough to prioritize anything. Taxes, mining, and farming revenue seem fairly straightforward (or maybe they're not and there is some horrible iceberg underneath). Trade is a bit mysterious though. Presumably, your investment dollar will go farther in provinces that have more valuable trade goods, but again this really doesn't get to the point of how trade revenue works. Although all the trade boosting buildings will generate revenue, any given building may be a good investment in one province and a poor investment in another. Roads, ports, wharfs, markets, all boost trade revenue but are they only raw multipliers or but do they may do they act in different ways in different contexts (setting aside the military usefulness of roads, strictly looking at money)?
- Trade is different from Merchant Income. For now remember this rule of thumb: sea trade (ports), connected with paved roads and large mines give the most income. If you have a cluster of rich port cities, move your capital there to negate corruption. For more indepth strategies, check out my guide on playing hotseats (but also on playing M2TW in general)

6. Do each of these trade building types interact with each other? (for example, do roads and ports increase the effectiveness of markets but not visa versa)
- All of them increase the export of the city in question. This has a double effect, because that export then becomes the import in another city. The building bonuses stack, you can see their effects in the city details as you add a building, it will show half-transparent carts which when you mouse over, will show the income value added to that settlement by the upgrade.

7. Does population size impact trade (not tax revenue)? Lets say that you have 2 identical provinces with the exact same natural resources and infrastructure and the only difference is that one has a higher population (set aside any benefit from its position relative to other provinces if one exists). Would adding a market to the larger population province have a bigger impact or would it be the same impact for both provinces?
- Population does not directly influence trade to my knowledge. Adding a market will give you an increase in tradeable goods, which is good.