Sally, I may have some more details about the Arps of New Holstein, Calumet County, as the result of research on the siblings of Elise Boie, my gg-grandmother. Her youngest sister was Wilhelmine Boie who married Albert Arps, as you noted.
Using the Castle Garden database, I believe I have found the family of John Arps Sr. arriving on 30 Apr 1849 from Germany on the vessel the Howard. He is listed as J. Arps, his wife as Sophia Arps, and the children matching those in Calumet County census records including the child John Arps, who was four years old. He in turn was the father of the four sons you have listed.
I am primarily interested in Albert Arps. He was not only in the hardware business, he also was involving in mining and served in the Colorado Legislature briefly according to a Who's Who entry. After their years in Ouray, Albert, Minnie and their son Elwyn settled in Denver. I can trace them through the 1930 Census. I would like to know their years of death and resting places if possible. Do you have anything more about him?
I would also like to know if Elwyn Arps was the husband of Louisa Ward Arps, a noted Colorado librarian, historian and author. Several pieces of data point in that direction but I really need confirmation.
I would appreciate receiving the e-mail address of Ellen Catharina Arps, the daughter of Gustav Arps, as I believe she could help me.