The Victoria County History describes the history of Barnet Town, East Barnet history, and Totteridge history, and Monken Hadley in some detail. The area formally known as Mimmside (that part of Barnet Town west of the High Street and north of Union Street) was part of South Mimms.
For 1870s Victorian Ordnance Survey maps there is www.old-maps.co.uk. These are slow to download, but can be searched using postcode and place name. There are also www.british-history.ac.uk versions of Ordnance Survey maps which are quicker to open.
The University of Leicester has made its collection of directories available online. There are four Kelly's Directories which cover the Barnet area (including Hadley, Arkley and Totteridge). Each has a description of Barnet at the time the directory was published, with a limited list of private residents, and then a list of tradespeople, including shopkeepers.
There are now a number of very good online libraries providing historical pictures of the Barnet area. Simply use the search facility with words like: Barnet, Arkley, Totteridge, and other relevant search terms.
For 20th century images try Corbis Picture Library
Francis Frith provides images from the post World War Two period.
For films from 1910 to the 1960s try British-Pathe.
'Barnet Past' Pamela Taylor, Historical Publications, 2002
'Finchley and Friern Barnet; a Pictorial History' Joanna Corden and Pamela Taylor, Phillimore and Co. Ltd, 1994
'Barnet in Old Photographs' compiled by Ian Norrie, Barnet and District Historical Society, 1993
'Historic Barnet' W.H Gelder, 1984