Hi, Wagnern!
I assume you are going to be using your Greek during the MTS for study of the Greek Testament and perhaps the Septuagint. In my opinion, it would be useful to have Latin, even if your period of theological study is prior to the late second century, because many secondary sources were written in Latin by later writers. Engaging with their work in the original language would only help your research and future applications.
Many Biblical Studies Ph.D. programs will require that another ancient language be obtained in addition to Greek and Hebrew, and Latin will be one of the options. To begin it during your MTS will put you another step forward. However, if Biblical Studies is your goal, you will also need Hebrew and, if you haven't yet begun, it would probably be best to begin Hebrew in your first year of the MTS and perhaps Latin in your second.
If you are interested in pursing a Ph.D. in Classics, then you would be able to concentrate in Greek or Latin. However, the post-baccalaureate descriptions I have seen say the strongest applications have both. I assume this is even more necessary at the doctoral level.