Rover,
I like the photo, as to what size; I don't know the environment you intend for it so I can't really offer much help there.
If it were for my home, 11 x 14 is probably a good print size and I'd use a 16 x 20 mat. White mat and a narrow black wood frame is my usual preference for my stuff and I think that would work well for this.
Are you settled on this orientation for the photo? I think it would work well as a horizontal with the shadow coming in from the lower right corner.
Rob