Eh, I'd explain if I'd understand it myself. The tests are NOT about the task at hand, but rather the most complicated way to keep "certain" people in and others out. Only certain select after-schools or buxibans have the actual data as to what goes into the tests.
For example, most are written not only all in Chinese, but as in Sung dynasty Chinese. Tha language for starters. Th econtents are a revered secret but with enough $$$ you can get into a certain school that has the "latest" -maybe 20 to 10 years old- information and pasts tests and the "official" books to memorize.
Most people take one or two years to memorize -yes, MEMORIZE- the books, and take the tests. Some people take tests six times before they pass.
The contents as said have not much to do with actual work, may probably even be wrong, but they want the answer they want, not the right one. Keep this in mind.
That is why I was suggesting enlisting, as you will avoid all these hassles.
I am sorry if I must discourage you but taking the Civil Service tests as an Overseas Chinese seems like a gargantuan task. Ask your relatives here. And it is really not worth it. Most people just wanted the 18% and retirement perks, but those are gone. Most young people are being hired on a contract base, so they are absolutely disposable... after they are overworked, of course.
Hiring in the public sector is practically frozen and last administration fired willy nilly, as part of a "plan" to reduce the overextended workforce. It is worse in the hospital/health provider sector.
In terms or jobs as researcher, I'd look into the Academia Sinica instead, or other biotecnology institutes, ITRI or any in Hsinchu. Maybe the universities, I'd start as an administrative and move on inside. They will value your language skills a lot more, better salaries and conditions, plus a more enriching environment.
If you wnat to, you can start going to class for Civil Sevice tests. But taking those tests is a full time job by itself. It is not like GRE or any other you may have experience with in the West. Most locals cannot hold a job and prepare for the tests at the same time. So this is a biggie. Do more research and ask your relatives. If you have family "inside" then Bob's your uncle. If you are from the South, sorry, tough luck.