I think you have made an exceptional mod that adds to Medieval Total War tremendously. Expanding is more difficult, and fielding armies more costly and realistic.
However, I feel that the threshold for distance to capital penalty is set too high. I am currently playing a long campaign as house of Jimenez-Borga (Spain). I was tasked by the pope, and successfully completed two crusades. One to Antioch and the other to Alexandria. However the distance to capital to penalty for each was beyond extreme. It exceeded 250% in both cases. I even used the console to make my crusading general exceedingly popular, over 120% governor's influence, quick built a church and town hall, dropped the tax rate to low, and had an 80% garrison. None of this however could raise public order above 0%. I was victim of a civil revolt in 2 turns, and withdrew my forces to the sea, and attacked Cyprus, where the 1/2 distance castle modifier made holding the area possible, as distance penalty was only 125%.
The problem is even if I converted a crusade target to 100% catholicism, and eliminated the religious unrest penalty, which was also significant, no reasonable general would be able to hold a crusade target if your capital is in Spain, or likely France, England, and Denmark as well. I assume a similar problem will exist with the new world, although I am nowhere near that point in the game yet. This is compounded as holding these areas is mandatory for the win conditions for some European powers.
The fix I propose for this is simple lower the max modifier for SOF_distance to 25 or 30, that would result in a max distance penalty of 125% or 150% respectively (max in vanilla is 80%). This would maintain the same rapid distance penalties for holding large empires as in your basic mod, as well as keep castles twice as easy to hold. However, a token crusade target would be at least possible, although still exceedingly difficult for a Western European faction to hold against civil unrest. Then you could at least focus your worries on your new angry Muslim neighbors.
As a side note I would not lower the maximum for religious unrest, as there already is a long term counter to it in the form of priests/imans.
I hope you consider this for the next version.
Regardless, a superb mod. Thanks for your hard work.