I have been to Grosshansdorf. It is a suburb of Hamburg. Most important it has it's own train station. That is important when commuting from the City. It is a quiet upscale place that is built around a very nice park. The is its selling feature - there are ponds and lots of trees.
My brother and I went there and 'stormed' the town. We bought all the postcards we could find. We also made the town jeweler very happy because he was the only one in town that had things we could purchase with the town name and emblem on them. We bought almost everything he had. There aren't any t-shirts or coffee mugs like you would find in almost any American city. Some people were very friendly and thought it was funny that our last name was Grosshans. Others didn't understand why we were so excited to be there.
I have a copy of the brochure that they give out about the town history but it does not say that the town was named after anyone specific. We did not have much time to spend there and it was the weekend so none of the official offices were open. We walked around in a local cemetery but did not see any headstones with the Grosshans name on them.