Good analysis overall. One thing you may have wrong is the degree home field will factor into the results. With its small student body, Northwestern rarely benefits from HF advantage, but in some ways has immunized itself (maybe because of the fact the visitors often are as numerous as the home crowd) from away game disadvantage. Over the last five years in conference, the Cats are 12-9 on the road and 10-11 at home. In the last 3 years, the Cats have lost 4 road conference games: in Madison, Columbus, Ann Arbor, and one possibly comparable game to a good Gopher team in the Twin Cities.
Since the weather forecast is for perfect conditions, I think whichever team wins can view the win as honest and not venue aided.
The advantage NU has over everyone at the home field is that it is the worst place to warm up at. There is literally zero atmosphere to the stadium and it isn't helped by the fact NU fans frequently aren't at kickoff and wander if somewhere between the 8-12 minute mark. It's a place that because of that lack of environment, NU can get out on you quick before a team can get itself going and by that time NU has built momentum that is hard to overcome as the stadium starts to fill.
Also, some of your road games have been against some pretty awful Cal, Purdue, and Illinois teams over the last 5 years (sprinkled in with some very mediocre Duke and Nebraska teams. NU's away games the last 5 years.
2017: Illinois (3-9), Nebraska (4-8), Maryland (4-8), Wisconsin (13-1), Duke (7-6) --> 3-2
2016: Iowa (8-5), MSU (3-9), OSU (11-2), Purdue (3-9), Minnesota (9-3) --> 3-2
2015: Duke (8-5), UM (10-3), Nebraska (6-7), Wisconsin (10-3) --> 3-1
2014: PSU (7-5), Minnesota (8-5), Iowa (7-6), ND (8-5), Purdue (3-9) --> 3-2
2013: Cal (1-11), Wisconsin (9-4), Iowa (8-5), Nebraska (9-4), Illinois (4-8) --> 2-3
Total away game record over last 5 years: 14-10
Away opponent total record last 5 years: 163 - 140 (53.7% win percentage)
You have also not started a season with an away game since 2012 at Syracuse and narrowly escaped a win there (42-41).
If this game was in late October or November when NU has a proven history of getting better and peaking, then I would be much more worried about this game. It is not and it is being played at what should be the largest opening game crowd for Purdue in nearly a decade or more. Your schedule has some nice away game years to it (2015 for example), but mostly the away games NU has had are to middle of the road or slightly better teams. In essence, NU is playing teams comparable or worse than them in most of their away games. Purdue, this season, should be in that category and I believe NU's win percentage over the last 5 years reflects what most fans believe to be the true odds of Purdue winning.....NU with a slight advantage but Purdue could easily win. It's a coin flip in essence.