I heartily recommend both the book and movie of Howl's Moving Castle, with the substantial caveat that you should not consider them related to each other. The plot is entirely unrelated and the only characters that have any similarity are Sophie, the castle, and its inhabitants.
I'd also suggest skipping Nausicaa entirely (it does nothing other Ghibli movies don't, and does them all very... flatly?), and recommend Mononoke, Howl, and Spirited Away.