Ditto on what Roll Tide said. I've only known one person to get her doctorate while active duty. It was Astronomy, maybe astrology, whats the difference, really? Serioulsy, she came through the Nuke pipeline as a full LT because of the time she spent in England getting her doctorate in Astrophysics. Doctorates are rare. It is more common to roll straight into a masters program out of college. The navy will foot the bill, all you need to do is commit the time. If you don't do it right after college, then after your JO sea tour, often your first shore tour is split with a stint as an ROTC commander, which you get your MS then, or a dedicated tour at Monterray.
As far as the quality of education in the pipeline. The navy manuals have the exact same information as many graduate level textbooks. I've worked on some homework at home and tried to figure a problem or two out and then remembered that there is a similar article in one of the manuals at work, with a little better explaination IMO. Funny, since the manuals at work are classified and my textbooks most definately are not. Despite the information being comparable, no college is going to give you graduate credit for you navy work. I've chalked that up to money. You have it, the college wants it.
You'll be promoted to LT so long as you have a pulse and can fog a mirror. LCDR is a board that you will make it through unless you are totally broke. I think that you are administratively separated if you fail to make LCDR after so much time. Those wickets and rules are lost to me. After LCDR, the competition gets severe. A lot of officers retire as LCDR at 20. O-gang promotion is all about your "window". If you make it in your window, with your peer group, then you're good. If it passes, then start looking at yourself and ask yourself why you missed it. I'm not going to say never, but you'll never make it if your window passes.
Even NUPOC, don't you have an ROTC commander that you can talk to? You should have a sponsor of some sort that their sole responsibility is to answer these questions. They would have more intimate details and more current information than a bunch of Navy has beens (Roll Tide

) and wannabe has beens (myself). Good luck.