1, are there more people with last name Lin in Taiwan than in Mainland?
No. Based on a 1996 study, there'reabout 14 million people with last name Lin in Mainland (85% of them live in Zhe Jiang, Fu Jian and Guang Dong provinces), and about 2 million people with last name Lin in Taiwan. So there're definitely more Lin people in Mainland than in Taiwan.
2. Are there more people with last name Lin in Taiwan than in Mainland percentage wise?
Yes. Lin is the second most common last name in Taiwan, and 16th most common last name in Mainland.
3. Amount all the people with last name Lin abroad, are there more Lin people from Taiwan than from Mainland?
Most likely. First of all, you'll more likely to meet a Taiwan Chinese than a Mainland Chinese simply because it's a lot easier for Taiwan Chinese to move/travel to US than Mainland Chinese. and since there're a higher concentration of Lin people, it's likely that the Mr. or Ms. Lin you meet is from Taiwan.
So to answer you question, yes, from a western perspective, people with Lin as their last name are more likely from Taiwan than Mainland.