I am expecting him to bat at number 5 position because Raina is back into CSK so he is the best ever batsmen at that position for CSK all the time and number 4 will be Rayudu so Curran at 5 and Dhoni at 6 will be good for destructive death overs for sure and more to add that left and right combo will work and shatter the bowlers line which has been missing in CSK last year due to the absence of Raina.
Raina at no.4 and Curran at no.5 will be really good for CSK. Because one of the issues they faced last time was the slow batting by middle-order (especially from Kedar Jadhav and MS Dhoni). They have very good top order (Robin Uthappa/Faf du Plessis) and it was due to the slow middle order that they lost so many matches last time, which they would have won otherwise. Raina and Curran should be able to take care of that.
I don't think Robbie will play as an opener for CSK because I guess he was bought as a backup opening batsman since they already have faf and Gaikwod to open the innings so in case of injury or poor performance may get him a chance or else he will be at the bench for this season.