Thinking about taking some of these in the subjects im stronger in to look more impressive to adcoms. To my knowledge, they are used more for college credit (like AP exams), but if I take some and score well does it look good to admissions?
SAT subject tests are used in admissions, not college credit, and only some universities consider them in admissions, and then it is often only for certain majors. You will need to look at the admission requirements for the colleges and degrees you are applying for, and see what they require in the way of SAT subject tests – whether they’re required, how many, and in what subjects. Beyond requirements, they can certainly look impressive if you do well in subjects related to your planned major.
For a start, check out this list from colleges using the common app: https://www.commonapp.org/Login#!PublicPages/ApplicationRequirements.