"…the leaded bourgeois type of a Times article…."
And old designation for the size of the typeface used by the London Times--the equivalent of about 8.5 point type.

"It's the pet story of the family, though I never thought of taking it seriously before."
There are numerous legends attached to old English homes and families, stories of hauntings or other mysterious happenings. Conan Doyle was inspired to write Hound when a friend told him a legend from Dartmoor that involved a hound.

Then, still keeping a hundred yards behind, we followed into Oxford Street and so down Regent Street.
Holmes and Watson would pass along Oxford Street from the bottom of the map [at left] and turn right on Regent Street at Oxford Circus. They would continue down Regent Street through Piccadilly Circus, make a left on Pall Mall, passing Trafalgar Square, and go on to The Strand and Charing Cross, where the (fictitious) Northumberland Hotel was located.

"…and then we will drop into one of the Bond Street picture galleries and fill in the time until we are due at the hotel."
On the map of Oxford Street, New Bond Street branches off to the right from Oxford Street, just below Regent Street, and leads into Old Bond Street where numerous art galleries are located. The Royal Academy of Art is nearby.