The internet has been a tremendous boon in undertaking research on Hereford. There are many sites which provide historical details and photographs: facebook pages, blogs, flickr, local government sites, britain from the air, etc.
You can find some of these in my post on Herefordshire’s Railways:
In addition, it is worth getting a flavour of the area you intend to model and sites about community life in the area are helpful, particularly when they contain photos and cover the historic period that you are interested in. See, for example: