Paul Varley's article is so stacked with rich data you have to break it down sentence by sentence.
"Nobunaga, for example, fought relatively few open-field battles" (Varley, p. 111).
I have some examples of the few open-field battles. Okehazama1560, Anegawa 1570, Nagashino 1575, Kizukawaguchi 1576 and 1578 (naval battles, Nobunaga lost to the Moori in 1576, but won in 78 with the iron clad ships). The battles are from the top of my head at the moment. If you know more, chime in.
As for forts, Nobunaga his first battle in 1547 was attacking an Imagawa fort. Battle of Mikawa Kihara Ohama. His first taste of blood was a success!
Tenka no Tame!