Two things I want an opinion on in regards to the rules.
1. Does Size (Hulking) apply to flying in the same way that it does normal movement? My instinct is to say yes (see page 43, the first paragraph of Flying Movement.)
2. Does the Black Carapace affect negative stealth modifiers in the same way that it affects to hit bonuses against the character?
1. No. The flyer trait specifies the new base movement that the character or creature uses. For example, a thing with the Flyer(10) trait would move as if it had an agility bonus of 10, so a half move of 10, full move 20 etc.
2. No. The Black Carapace only negates the bonus to hit. Space marines still suffer the penalty to stealth from being hulking.
Hope that helps.