Hi, Meursault.
In 10a, the definition is "fashion" as a verb, so the second letter is not an H.
In 16a, the second letter and the sixth are both in the thematic phrase and omitted from the wordplay, so "hands over" simply means that the two letters implied by the rest of the wordplay are surrounded by H and H for "hands".
In 7d, "from the south" applies to all the wordplay, so you have a four-letter sea surrounded by a three-letter word that can mean "resident" in the sense of "a native or inhabitant", all reversed.