By Alan Smith Brennan Johnson has promised Tottenham fans that he is only getting started. And with Spurs suddenly able to call on their full cast of attackers following injuries and international commitments, the £47.5m summer signing believes Ange Postecoglou’s team are about to hit new heights. Johnson fired home in the 96th minute to break Brighton hearts on Saturday, converting Son Heung-Min’s low cross. It was his third league goal of the season and the 22-year-old admits he has needed time to acclimatise since joining from Nottingham Forest. “I don’t think anyone has seen the best of me…