Of course,There is a locker.Check the linked page which is including Train schedule.
Namba - Station Information | Nankai Electric Railway
Nanba is the biggest station in Osaka Minami district.like Shinjuku or Ikebukuro in Tokyo.
I recommend walking around there.
Kobe is better for Honey Moon.As Firebird stated before,famous for Harbour Area
and night view.I recommend strongly one day tour.Roughly 50 minutes train ride from Osaka.