First time sugesting something, and i feel like many of the sugestions will not be very welcome. But i think they would make the game more fair.
English is not my first language and i didnt have time to do a well structured text, so be kind.

-Market:
This sugestion will make it impossible to abusively transfer resources between kingdoms, as has happened on several occasions where kingdoms were buying resources at the maximum price and then selling them for the minimum price between friendly kingdoms.

When selling the products, you can only choose the amount to be sold but, the price should be fixed.
When someone buys resources, the gold used should be distributed by percentage of the total amount of that resource avaliable.

Spell casting:
I understand that with the number of players, the existence of MP makes sense, but it doesn't make sense that doing MP is more rewarding than directly casting spells. My sugestion would be that it should be removed from the game later on.. but for until we have more players it makes sense to keep it...
I've been playing as an elf for the last few rounds and to do the basic spells, i would produce mp first and then cast them since its more efficient that way, shouldnt be like that.
The resource tranforming spells, with the existence of the market, i would sugest that they should be removed from the game.
This would be a good oportunity to introduce new spells. Like one that was commented before on the chat by ves (i think he said it as a joke but i like the ideia), it's enchanting weapons, you cast a spell that uses the weapons on the armoury to aid in defending attacks. (Or some other spells, this was just an example)
One other problem with the spells is how useless some of them are.
The ofensive spells dont do enough damage, and the possibility of them being canceled is also a problem.
I would recomend instead of creating a counter to freeze, to actually remove the other counters for spells.
A big example of how pointless this is ice storm, that can be cancelled by one of the basic spells, that can be done by using mp.

Other changes that can be done is the mages rest system. Have in mind that this is a biased opinion since i always play as an elf. I would like to sugest the ideia of having the mages being able to cast all kinds of spells, and use the ATC to rest them from casting.
I would make sugestions on other races, but i dont know them that well...

Strategy
I would like to know some statisticts regarding the strategies used.
In my mind (i can be mistaken), there are very few strategies that are currently used, no strat, quick retreat and the racial strategies. The others if are really not used often, should be readjusted in order to have a bigger impact on attacks.

Quick Retreat is a tech that i would change in a different way that the one that is going to be tested in the mini round.
QR as the description says, should reduce the probability of winning the attack.
As such my sugestion would be to allow anyone who choose's it, to determin how much of their army they are accepting as a loss (like 30% to 70%). As soon as that percentage is reached the remaining army would march home and the attack would be considered as a loss.

Now for the most discussed change requests from the chat:
-Resources giving KS
its not important enough, and its not really a problem. It gives ks for everyone, so if it stays, it stays, if not, its also ok.
-Attacking and retailing restrictions
They should all be removed. I would add a new system that gave extra penalities for attacking below 50% and above 200%, but i would not make it impossible to attack.
-Land and castles gained in attacks
The 8%-12% is a bad idea. In the start of the round it will make attacking not very atractive and would make farming even more rewarding. Even later on it would be more rewarding to farm than to attack.
That leaves us with the abuse on the 1 castle 200 land problem. It can easelly be solved, since on castle only can build on 45 of land, if someone has over 45 of land and 1 castle, it would loose all the excessive land over 45.
The other existing problem is the 2 castles kingdoms that are broken in half, and are impossibilitated from destroing castles. I would solve this situations by reversing to a 10% chance of lossing a castle for each castle. I know its not perfect but its a better sistem.
-Taxes on trades
Just remove it all. If i'm paying taxes i want a good health sistem, good roads and public services working like a charm. If none of them exists in thardferr, then i see no point in having taxes.
-Cli
I think is fair that cli exists, but i would extend the retail period to 24 hours again, and reduce the cli duration to less than the transport tech. If you can be 24/7 under protection from cli it makes the game boring and since the player base is so small it comes to a point where there are no targets.

-At last i'll talk a little on the castle passing situation.
Its not gonna stop, ever. As the game is now there is no way to avoid it.
I think its better to assume that its part of the game...

I hope some of this sugestions help somehow to make the game better...