During Fox's tenure, Carolina had:
404 RB rushing attempts in 2007 - 10th in NFL
389 RB rushing attempts in 2006 - 21st in NFL
449 RB rushing attempts in 2005 - 8th in NFL
392 RB rushing attempts in 2004 - 19th in NFL
465 RB rushing attempts in 2003 - 4th in NFL
394 RB rushing attempts in 2002 - 10th in NFL
90 RB targets in 2007 - 23rd in NFL
127 RB targets in 2006 - 8th in NFL
103 RB targets in 2005 - 13th in NFL
106 RB targets in 2004 - 15th in NFL
89 RB targets in 2003 - 27th in NFL
116 RB targets in 2002 - 20th in NFL
Assuming their running game is at least a bit improved due to improved OL and the upgrade from Foster to Stewart, plus a better passing game, perhaps we can expect 420 RB rushing attempts or so. More is possible, but I wouldn't count on it, since 4 of 6 seasons under Fox there have been 404 or fewer. Last year, Foster and Williams combined for 97% of the RB rushing attempts.
I think with Delhomme back and improved WRs, they should throw to the RBs more than last year, but not as often as in 2006. I think 100 targets is reasonable. Last year, Foster and Williams combined for 81% of the RB targets.
So... it seems reasonable to think Williams and Stewart will split around 410 carries and 80 targets. I could see it like this:
Williams 220 carries and 60 targets
Stewart 190 carries and 20 targets
An important question is who will get red zone and goal line opportunities. I suspect those will also be split, at least early, and only focused on one player if one of them outperforms the other in the early going.
I think Williams is good value at his ADP.