I'm glad to see this continuing, it was a very interest story so far. Please write more.
I seem to remember something about reading more of Luna's letter when he was wearing different uniforms, but I don't seem to remember that from this time.
There are only a few things Harry needs to figure out to become very dangerous: warding (and I mean something simple that can turn a torpedo into a shield buster-if there was only some rune that harry knew just like the skin on his face—though a notice-me-not on a starship has possibilities), legamancy (snooping on diplomats for fun and profit, though I guess the Federation is already all over that), and portkeys/apperation (a strike team going through the shields of an enemy ship) or possibly even just a point-me spell (point me stealthed klingon vessel). Some of these he has a decent chance of figuring out by himself.