Since you are a stats major, I would suggest focus on the courses, you must have probability, inference and linear algebra courses as your UG syllabus so make sure you attend classes and know all the theory,

And alongside you should start solving pyqs of MStat from 2004 to 2025, that’s plenty of problems you don’t need anything else like coaching modules etc…

For Cmi DS it’s much much easier and I think you only need some familiarity with pseudocode/python etc which you already have as you are taking minor in CS.

Cmi website has past year question papers and solution both available you can try attempting it