Lukaku showed a lot at West Brom, but that's a long way away from being ready to lead the line as a lone striker for Chelsea. If he doesn't get better at holding the ball and retaining possession then I think he'll struggle in your formation without more support. Torres and Ba are decent, but so are Welbeck and Hernandez, and it says a lot when Chelsea's two first choice strikers are being compared to Utd's backups.
Cahill again isn't bad, but given how regularly he plays CB for you he should be a way ahead of Smalling and Jones, who play RB and CM as often as they play CB for us. And like you say, after Cahill you are looking at young players with little or no experience.
The midfield is quality I agree. Although again lacking depth in the anchor role, with Essien looking a shadow of the player he was. Does make me wonder why your biggest signing of the summer was Schurrle, when you have so much quality in his position and are so thin on the ground up front and at the back. Still, I guess it makes about as much sense as us fixing our midfield issues by signing RVP last summer!