Presenting the Big Ten Tourney Bracket (view the image to embiggen):
Michigan will face the highest seed that wins from Wednesday's game. So, if seeds meant anything in such an evenly matched conference, if the two top seeds win, Michigan would face NU and Minnesota would face Iowa. But if NU were to lose to Indiana, but Iowa still wins, Michigan would face Iowa and Minnesota would face the Hoosiers. Hope that all makes sense.
Yes, that is no Ohio State playing at home in the field. Crowds may be miniscule for this one. NU and Iowa aren't known for fans traveling well, although Northwestern did have a few more at Michigan than expected. Not sure what to expect from Purdue, but I also imagine not many.
Indiana should see a good contingent up from Bloomington, and Minnesota normally has a good fan base. The question for Minnesota is the travel time. The Gopher team is actually staying in Columbus and not returning home. They just wrapped up a series there and it wasn't worth busing them back and forth.