AI traders also contribute greatly to the prosperity of the hanse, especially in the first few years, they are important suppliers and mediators. It is not necessary to kill them all even using the turkish building technique. So it is misleading that you have to catch all the white ships in the ealy stage, in fact , you may have finished the game without catching one single white ship. However, they do build white plants and houses to destroy the "pristine" green land, it is necessary to demonish the white buldings in time to avoid roads creating. It is a bug that solve this problem, firstly you have to at least have a plant/house in the town, left click on your plant/house once and then left click twice on the AI trader’s plant/house, you will be capable to demonish the white plant/house just like erasing your own plant/house .
Starting closer to 1300 also means less houses which belonged to the town, in other words , more "pristine" green land in each town, that is crucial for turkish building. If you start in 1400, it is apparent that more houses and less green land available in the town than that of the year 1300.
The bribery did not go to the town coffers . The method that "levy extra tax" to bankrupt a competitor only works in the two new towns which were built by your own effort, you may infinitely levy extra tax to bankrupt the merchant who had opened an office in the new towns in the charge of you, but before that, you have to hide your assets to mininize your share of extra tax. But you do not have to bankrupt them, just for fun.
AI players start building their own houses as soon as the game starts especially in Cologne, Scarborough, Gronningen , Bremen,Ripen,Torun, Aalborg,Bergen,Ladoga and Novgorod, but it does not mean that you can ignore the other towns. It is very difficult to remain all the "pristine" green land intact because AI traders build houses in some town even before you finally get a permission to open an office in that town, just like what happened in Cologne, Torun and Scarborough. So in my opinon the best hometown for turkish building is Cologne, but it depends .
A player who named “Zhuzaijianghu” once sweeped all the white ships in the first three months ( in Jul 30, 1300 ) and remained all the green lands intact except scarborough, pitifully he did that in the local language edition so in the save file the towns and ships' names did not appear correctly in the English editon, but it did work in all other aspects.