This year, I’m taking the Biology and Math Level 2 Subject Test and I am planning to take more in the next couple of years. Does it look bad to colleges to take a lot of SAT Subject Tests?
Thanks! 
Not really, but once you get to a certain number, I do not think they will care or matter as much in the admissions process.
2 or 3 is the standard, beyond that, diminishing returns.
Most colleges ask for 2. Some ask for 3. I think if you have 3-4 successful tests under your belt, you should be fine. Distribution-wise, however, you should take an SAT 2 in language, history, or english because most schools ask to see an SAT 2 in the humanities and an SAT 2 in sci/math.
Perhaps depends on your application self-image. I mean if you are a science person, then take some subject tests on sciences. Otherwise go for humanities. Let’s say you aim for biology, so a US History subject test might become useless in your application story.