Why do you all feel he will score 25+ goals? He scored around that last season ok that's fine. Before that in around the same number of games he scored 18, 10, 15 per season etc.
I can't see how moving to you will improve his score. Your track record with Depay, Falcao, di Maria, Ibrahimovic, Pogba all showed they scored less goals than what they did before moving. Honest question, what makes Lukaku going against that trend? From his one dimensional style of play and his previous track record, to me he'll score around 15 in the league.