Here is a directory of Catholic churches in Taiwan
I do not know whether a Catholic priest would agree to celebrate a wedding that did not involve at least one of the participants being Catholic. If he would, you should expect to be required to do Pre-Cana, or preparation for marriage class
In my own case, I am Catholic, and was fortunate to befriend 2 Roman Catholic seminarians who were in my class at Shita (NTNU) when I tried to learn Chinese once upon a time. They were both from Italy and had the same name - we called them, the Two Paolo's. We kept in touch after I bombed out of NTNU and when I finally popped the question to my girlfriend years later, I asked one of the (now) Fr Paolo's to preside. I happened to know the parish church of the area where I live, and even though there are no English masses at that church, the parish priest (who was from Spain) at the time happened to be a buddy of Fr Paolo from another Chinese class he had. So, when Fr Paolo and I approached him about using the chapel, the parish priest was happy to accommodate us.
For our wedding banquet, my wife found a good deal at the Intercontinental Hotel in the Combat Zone. It's now called the Imperial Hotel. Hotels are very organized when it comes to weddings, and if you plan it right, you should make a profit. (We came away with a slight profit.) This is because the guests are expected to come with Red Envelopes of cash.
The hotel seemed to know everything down to the little details i would have never considered: the reception table came equipped with a cashbox and money counter, my sister-in-law (who is an accountant, thank heavens) stepped up and handled the counting of the cash and payment to the hotel, a room was provided just for this purpose and everything was settled by the time the last guest took the last candy from the basket at the end of the evening.
So, when you do your calculation, think about how many guests you will invite who understand that they are paying their way. And book a venue that is appropriate - it doesn't have to be a hotel - but it should reflect how much you respect and honor the families involved.
I remember visiting a hot spring resort in Yilan that had a chapel by the water. It was a non-denominational chapel, and was expressly for weddings held at the hotel. There was a similar chapel at a hotel I stayed in at Okinawa when I was there for a company trip.