Regarding the infield, I think the unknown is Miranda. If he forces his way on the roster, he will get playing time, not just be a backup and then there are too many players for the three positions. If the Twins are content to send him back to St. Paul, then having Arraez, Urshela, Correa and Polanco to cover the three infield positions is enough and adding Gordon as a utility guy who can sub in center field and pinch run makes sense. With Miranda on 26 (27-28?) man roster, it makes Arraez expendable.
As far as a fourth outfielder, well what about a third outfielder? Right now, Kepler and Buxton are locks and we don't know who will man left field. It could be Kirilloff, but I would really like to see him get the majority of innings at first base. Larnach would be my preference to play left, particularly since he hits left handed. The Twins have acquired three right handed bats making them lean more to the right than they have in some time, particularly if Arraez is traded.