The short answer is: yes, you are right, a course on modal logic would be the one that probably will relate a little to a philosophy of religion course (it will help you understand e.g. modal ontological arguments).

But I think it is worth saying a bit more. I'd be a little worried if one of my first-year students said "I'm primarily interested in the philosophy of X" for any X. After all, philosophy is a subject where topics don't compartmentalize easily but connect up in deep and unexpected ways. Beginners should be exploring widely, and leaving themselves open to being gripped by all kinds of problems -- what I like at this stage is a student who says "the philosophy of Y is really exciting: that's what I want to do " one week, and then comes back three weeks later and says "wow, this philosophy of Z course is amazing".

And I'd be particularly worried if someone focussed too hard too early on a small area of applied philosophy like the philosophy of religion. This is a pretty narrow specialist area, which not all philosophy departments even think particularly worth teaching (e.g. mine doesn't offer a course apart from a few lectures on Hume's Dialogues). So, for the moment, do keep your interests wide! And then it is probably a good idea to do a fair amount more logic, as that will keep cropping up as useful background which is taken for granted in work across a range of areas of philosophy.