I'm late to this thread, so I won't have much new to add.
Year one: I think just making a bowl should be the expectation. Anything better is gravy. I think Nebraska could realistically win more than six games in the regular season, but the first year is more about implementing the system than wins and losses. As we all know, the schedule is tough too.
Years two and three: In one of these two seasons, I expect a big jump. Not necessarily a playoff or national title jump, but a dramatic increase in on-field performance. By the end of year three, you generally know how good or bad a coach can be. There are exceptions, but there aren't many coaches winning seven or eight games a year that have a huge jump in year six or later.