McCaffrey got 23 carries per game and 3.5 receptions per game in college.
Stewart had just under 20 combined rushes/receptions per game in 2015.
I think you're right that my numbers were a little high - have to account for fewer plays/game in the NFL and increased physicality of the NFL game.
My thinking is he will average ~15 touches / game in the NFL. In the NFL, that is likely to be weighted a little heavier towards receptions than rushes vs. his college experience, given his size and athletic profile.
So maybe 10-12 carries a game, 3-5 receptions per game? Maybe you only throw him out there on punt returns and let other backs/WRs handle KO duties.
Either way, I think he will get more than enough usage - with the Panthers or with another team - to justify being a mid-first pick.
The Panthers barely used their first round picks the last two seasons.