Brighton will be well organised, and will try to make sure they aren't exposed to any quick counter attacks (i.e. don't expect to see their full backs getting ahead of the play). If the Liverpool game is anything to go by, they won't change their tactics much if they ship an early goal.
This could be a real grind as we'll be up against 10 men behind the ball for most of the match and time wasting from the outset. I think Brighton's full backs are a weak point, so I expect Martial and Young (if he plays RB) to be key. The centre of their defence is a strong point, so we need to find ways to drag them out of position (Lingard playing in that point of the diamond role perhaps). If we're deep into the game and haven't made the breakthrough, then Mata could have a role to play.
They aren't a very creative side, so we shouldn't have too many problems defensively, except perhaps from set pieces.
To my mind, a 1-0 or 2-0 win is the most likely outcome.