I don't think Lowry, ibaka and Fields will be as productive without a plethora of better scorers around them. You have 3 4th options in your staring 5. That's my big objection.
So you're saying they'd be less effective if they take more shots?
You might be right...its pretty difficult to say. They're all young though, and considering Fields' consistency, Ibaka's incredible improvement in only 1 year, and Lowry's improvement from last year to this year, especially in scoring..I think it is just as feasible that they'd be able to maintain their current efficacy, and possibly (I'd say most likely in the case of Ibaka) improve on their impact further.
The biggest concern I think is actually Paul Pierce. Although all 5 starters project to be 10 ppg scorers, Paul Pierce is a significantly worse player when he tries to be a hero for a whole game. If his FGA's go up significantly, I think his FG% drops just as significantly...so it will be important that some of these guys come through.
Oh god, here come the spreadsheets 
Hey, I just like looking at them. Its a way to keep busy when nothing is going on...playing with MPG, looking at how per minute production fluctuates..looking at %'s...this stuff brings out the excel nerd in me.