The Smallest Happy Number

With subtle wit, great imagination and evocative sentiment, this enchanting tale follows a formative and idealistic period of Billy's life in the late '70s before catching up with him in the present day.
It's 1978 and it's a time when Billy experiences his first stirrings of romance and his first taste of bereavement; a time when he takes on a fight for justice that will live with him for the rest of his life; and a time when he discovers that friendship and love defy the boundaries of age.

What is the link between the derelict factory and the pristine Austin Seven Swallow under wraps in Ada's garage?

Will Ada ever succumb to neighbour Oved's romantic overture?

And what is the reward awaiting Billy and Andy for helping out in Ada's garden?