ROTC-Navy Questions

Hi! So, I’m considering joining the NROTC program, but I have a few questions. I’m planning on doing the four years with the program and I was wondering, can I join Navy JAG a year later and go to law school or do I have to finish my four years in a different department? Thanks in advance!

Also, I have more questions:
Would I have to study a certain major? When would I sign up before or after I get accepted to that specific college? What are the chances of getting the scholarship? What can I do to improve my chances? Thanks again!