Health is obviously a concern. Even though he's penciled in as a KR/PR I'm not sure they'll do it.. it just doesn't make sense but they just might have him return kicks and subject him to a higher...
I don't know that Seattle will use Harvin on PR/KR considering his injury history and their lack of depth at the WR position after losing Tate and Rice in the off-season.
Thomas Jones, Reggie Bush, Tiki Barber, Marshall Faulk (I can name quite a few others) are all high profile RB's that had to learn and adjust to the NFL before peaking talent wise.
You use the franchise tag, and use him up for one more year. Make sure that you aren't giving away a top 10 talent at the position, or make him prove he's worth a new contract to not only your team...
Panthers franchise got hand-cuffed, beaten, and royally screwed by Marty Hurney with the moves and contracts he handed out the few years prior to his exit.
Fighting for your division (being competitive) is exactly what they are attempting to do, and would hope for, upon drafting their franchise QB in year 2-3 for most teams.