Here's a very crude map (not mine!) of the situation in Taiwan in 1685. Note the three existing European outposts and the areas that will be contested during the second phase of the Scramble for Taiwan. Hopefully this makes things a little easier to visualize for people who aren't so familiar with the geography.
Just discovered this, and I must say, great story!
Looking at Taiwan, the Dutch and Spanish forts are really close to each other-I think they're going to be pretty much occupied until one kicks the other out, leaving the English with a few years to expand their control over south Taiwan.
Also, I think it likely that Taiwan still ends up Han Chinese, especially if the Dutch or British win. Both will probably want to set up plantations on Taiwan, and the Chinese mainland is still the closest source of cheap labor. (I know the Qing court banned emigration...they banned emigration to the US in the 19th century, and look how that turned out). The Spanish might be an exception to this pattern-I can see them importing Filipinos, whose language/culture will probably merge with that of the Taiwan aborigines. I think there would still be a large ethnic Han presence though.