I think it's unfair to expect something like 1700 rushing yards or 2000 total yards out of Elliott since the only way he puts up something like that is if he gets overworked, which we clearly shouldn't want.
If we gave him 392 carries and 57 receptions like we gave Murray in 2014 I'm certain we'd see at least 2000 total yards and upwards of about 2400, nobody in their right mind wants to see Elliott given that kind of workload though. Assuming he gets about 280-300 carries and about 30 catches I think a fair expectation would be somewhere around 1300-1500 rushing yards, 250-300 receiving yards and about 10-12 TD's.
It's important to note that Gurley and Peterson only averaged about 17 or so carries a game in their rookie years, which would be 272 if Elliott plays all 16 games. I think he probably goes beyond that but not by a whole lot.
Anybody expecting over 1500 yards is just setting themselves up for disappointment since that'd mean he had way too many carries or averaged about 5 YPC. I don't think it's impossible that he averages 5 YPC but it's too much to expect that right off the bat.