UPDATE:
I have just completed the backround image for the poster and I am now in the process of creating the rank devices. I plan on creating 10 of them, to include O-1 Ensign, O-2 Lieutenant (Junior Grade), O-3 Lieutenant, O-4 Lieutenant Commander, O-5 Commander, O-6 Captain, O-7 Commodore, O-8 Rear Admiral, O-9 Admiral and O-10 Grand Admiral.
I'm still on the fence about including the ranks of Moff and Grand Moff, since they seem to me to be politically appointed ranks, since it has been established that Moffs are in charge of systems sectors and Grand Moffs are charged with Priority Sectors. Also these appointments were generally created to fill the vacancy left open when Emperor Palpatine dissolved the Galactic Senate. As such, they would really have nothing to do with the "rank and fold" structure of the Navy.
Opinions and comments are more than welcome on this issue. Please let me know what you think.