It's a little difficult to describe Nicholas because he's so in-the-background, but I've made a few notes about his appearance and relative youth (he's older than Jack but probably still in his twenties).

I don't know that the characters are really in fear of their lives -- Clare and Jack both trust to Jack's abilities, and Graveworthy is generally reasonably fearless -- but I can have a look at the launch scene, that might help soften the anticlimax a little.

I think flourishing is right, isn't it? That's the way I've always read it. "Tar" is a slang term for sailor.