No extra leg-room with preferred seats, other than bulk-head. Or if there is it's minimal.

But bulk-head also have trays in arms, so a bit narrower.

Windows have less foot width as fuselage narrows. That would be the thing that would bother me most on such a long (for a Q400) flight.

So I'd get two together so you can switch, and also avoid getting paired with an above-average sized seat-mate.