Huge garden hedge
Having just purchased a house from a gentleman who had much more of a green thumb than mine, I have inherited an incredibly large hedge in the garden. I have attached some pictures below. I would welcome any advice as to how to take care of it. It is so big that I don't know how to even go about starting to take care of it. It is extending into neighbors' house and also extending over the fence at the back of the house. It is about 30 feet wide and roughly 20 feet high. It must be 3-5 feet deep.
Is it something which requires professional maintenance? If so, any idea as to what is required and how much it will cost?
Many thanks in advance.