The runners up only qualify for the Europa league if the winners have qualified for the champions league. So Dundee Utd would have to finish 2nd which is not looking likely so for County to get into Europe they need to win the cup.
The cup winners actually take the highest Europa league entry spot and would go in to it at a later round than Hibs/Motherwell and Dundee Utd, I think they would go into the round before the group stages like Hearts did last year and as they would be unseeded they would face a pretty decent team, which is prob what they would want.
Also Victoria Park is not really up to Europa league standards as they don't allow standing spectators so that would severly limit the capacity, if they do qualify for Europe you would most likely find that they play their game in Inverness.