Not to be a contrarian, but the decision about ferry vs plane also depends on if you're trust transiting through HEL or spending time in Helsinki city. If so, the baggage collection and trip to Helsinki port also weighs into it. Considering you can do 50min connections in HEL, I much prefer the ~20min flight.
Re award seats, I have obtained them fairly easily over the last 10y or so through QFF - but annoyingly, yes you have to call to add them to your itinerary. TLL as a destination isn't loaded on the QF website.