Been checking back for the first appearance of William in the Ozzie records, and found a few omissions. The IGI has the marriage and the following children
Batch Number: 0960338
WILLIAM THOROUGHGOOD - Male Marriage: 1856 Stockton, New South Wales, Australia
Batch Number: 0960338
MARY ANN THOROUGHGOOD - Birth: 1857 Stockton, NSW, md as Thorogood Wm Latham 1875 (d 1938)
HANNAH THOROUGHGOOD - Birth: 1862 Stockton, New South Wales, (d 1947)
THOMAS THOROUGHGOOD - Birth: 1863 Stockton, New South Wales, (d 7 June 1938)
SAMUEL THOROUGHGOOD - Birth: 1866 Stockton, New South Wales, (d 29 Mar 1930)
BENJAMIN THOROUGHGOOD -Birth: 1870 Stockton, New South Wales (d 23 Aug 1927)
A boating record says Benjamin Thoroughgood (1870-1927) was born at Clarencetown.
Batch Number: 0960361
ELIZABETH THOROUGHGOOD - Birth: 1857 Stockton, N S W, Md Wm J Smith 1882
SUSAN THOROUGHGOOD - Birth: 1859 Stockton, N S W, Md Thomas Latham 1877 (d 1917)
ROSE A THOROUGHGOOD - Birth: 1868 Stockton, New South Wales,
MATILDA JANE THOROUGHGOOD - Birth: 1873 Stockton, New South Wales, (d 1874)
It puts his marriage earlier several years earlier than you have (1856 not 1862) adds Mary Ann (1857 unless she was also known as Elizabeth) to your list, but missing is the 1864 Elizabeth. It wouldn't be the first time the IGI got things wrong, but its worth checking the old Stockton / Clarencetown records again in the hope that there was an earlier marriage certificate with much more information on it.
As for Preston Barracks, (not to be confused with the barracks in Preston Lancs) its a bit of a no hope-er because the 10th & 18th Dragoons were there in 1814, and it could be that their blacksmith went where ever the those regiments were posted.
Also noted that there is a complete dynasty of blacksmiths with the Thoroughgood surname, most with their roots in East Anglia or Ireland.
Roy G