I agree that it is best to avoid the last name of Cohen. While there are exceptions (there are exceptions to everything), someone with the last name of Cohen (or Kahn, Kagan, Kohn, Cowen, Corwin, or many variations) is likely to be a member of the priestly tribe, and if they are observant, may observe the prohibition against visiting a cemetery, or even entering a room where there is a dead body, but there are some exceptions for relatives. So, skip the last name Cohen. It will just be simpler. And you might as well skip the last name of Levi (or Levy or variants thereof) which signifies someone descended from the same Levi tribe (a Levite), but not from Aaron himself, from whom Cohanim are descended. So, to simplify, all Cohen are descended from the Levi tribe, but not all members of the Levi tribe are Cohanim.
One tradition that remains remains common among Jews is to have a simple casket. You can easily add a level of authenticity by adding (when appropriate) that the decedent had always talked about wanting a simple casket. The simplest will not have any metal hardware at all, but that is only common these days among the very observant. But ornate caskets are unusual, and I have never attended a Jewish funeral which was open casket (so ornate interiors are not likely to be offered). It is not unusual for the ceremony to be at the graveside. Jewish funerals also take place quickly. The next day is common. Not on Saturdays. Not on Friday afternoons. And since September is coming, avoid the time period beginning a few days before Rosh Hashonah (September 13 - 15 in 2015) and ending with Yom Kippur (September 22-23 in 2015). Yes, people die then also, but it will just be simpler.
A very large number of Old Testament names are now in favor by Christians, particularly Evangelicals. And definitely among the Amish, Mennonites, and other Anabaptist groups.
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008