Congrats to the newly wed to be!
Basically I think you have figured out what to do to get married in both places.
But from what I learnt from other people's feedback,I'd suggest it's easier and quickier to get married in Taiwan.
I get the impression that the VFS office have a turnaround time of a week or less for simple applications, compared to 8 weeks for applications inside Britain.
Yes, don't forget the golden rule; time is money and money is time!
how posssible is it for me to fly to Taiwan, marry and return to the UK within the 2 weeks holdiday that I have got?
It's very likely to have everything done with 2 weeks, if it's well-planned:)
Btw, there is another forum which may be useful for your finance (http://www.hellouk.org/forum/
Lots of similar English-Taiwanese marriage examples including the experience of sharing how to apply UK spouse visa and PR can be found there.
However it's mainly discussed in Chinese.
Have a happy life!