Hello, I am Li Zesong from Hangzhou. Here are the answers to your questions.
First: Generally speaking, except for the homes of officials, I do not recommend the use of arch decoration.
Second: The arch shape is similar to a tombstone.
Third: You can hang the gourd in the middle of the arch or on both sides, or you can place unicorns on both sides, one on the left and one on the left, facing each other.
Hope this helps.