If you go full time, you get the full pay and benefits that match your rank. You must usually be available for world-wide assignment.
If you want to go to law school, for many services you could apply after you've been commissioned for a few years and if selected (its a very selective process, so you've got to have a really good record), you would attend a civilian law school while also getting your military pay - its a great deal. For each year of law school, you usually owe 2-3 years of service. Many services actually look to hire people after law school once they've passed the bar and sometimes they can come in as an O-2 or O-3 and don't have to start as an O-1.
I suggest you call your local recruiter and see what they can tell you.
Check out the Coast Guard Academy, too. It's the smallest of the services academies and does not require a Congressional appointment.
With respect to your goal to be a lawyer, I recommend the following website: https://www.jag.navy.mil/careers_/careers/opportunities_da.html
This will give you a step by step process on how to become a Navy lawyer, which will give you experience and possibly allow you to merge these two careers into one (Naval officer and lawyer). I am not a lawyer myself, but I have worked with many during my naval career. They are always busy, but they all seem very satisfied with their career choices and they promote fairly quickly.
I hope this helps.
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