Lewandowski can make a good contribution. Yes, if you say he played well in Germany you can say "Spain is a different football", but Robert also played well in the Champions League and scored many goals, so for him it does not matter in which league and against which team to play, he can adapt in Barcelona
With a tic tac scheme? I don't think so, that must long time adaptation, this is a big difference between Barcelona and Munchen using the long passing ball to Lewa. maybe a little stiff when first time playing with the strategy where he must run and move quickly to outwit the opponent. Exception if he only stands in front without picking up the ball.
Perhaps Robert is not a player who adapts very quickly. But I'm sure it won't take him very long, the first two games, or even one will be uncomfortable for him, but I think before the season in training he can already feel at ease, so I'm not worried about his game. He is a very talented player despite his age, it will be a very good acquisition for Barcelona