Just a few more additions to the reading stack:
Osprey's New Vanguard series, # 170. It is a good overview of the tanks - and just tanks - used in the Spanish Civil War. It is a slim volume at 48 pages, but it has some good photos and color plates.
And, another one:
Also by Osprey, this is Aircraft of the Aces # 106. 96 pages, with more photos, many more color plates, and more information than their more slim cousins. The historical information about the aces covered by each volume gives a lot of potential scenario fodder...