That is an interesting article. I would be willing to bet that your shop will question the 6 degrees caster. I knew was large but did not realize it was that large. I would have said 4 degrees. Here is an article that I found:
Caster, Camber, Toe
I do not like or agree with shopping cart example but that is a small part of the discussion.
Bottom line, ask the shop what they will set your caster at and go from there.