Hi York,
My last name is also Li or Lee, also from Taishang but that's not mean we are related. You have made great progress by knowing the name of your ancestors and knowing they are from Taishan which is not that big, now you have to figure it out which city in Taishan for example Doushanzhen, Duhuzhen, etc. Zhenjiang means city. Now, once you have the name of the city you need to find a township. Townships are small communities in the cities where people living there has the same last names because women when they get married move in with their husband!s family that's why the hole township has the same last name, so once you know the city look at the township with the last name of your ancestor I'm sure there aren't many and once on the township then is useful to talk to the locals cause they certainly know each other and if not, they will ask others die you because connecting to families is very important for Chinese.
Just make sure to have the names in Chinese and other info such ad photos, documents and a translator taisanese-mandarin with you. You should go to China once you know the city in Taishan where your ancestor is from because there no reliable info on the web after you know the city and don't pay anyone from abroad they will ripped you off.
So, good luck! And if you find your ancestor share it with us 'cause myself I'm looking for my great great grandparent who migrated to the Uk with his brother, but unlike you I have nothing, only the name :(
Well, good luck!