Miyajima is small enough to cover by foot, and there are English-language signs throughout the island. Taxis can be taken from the pier to the hotels and residential areas, but not the tourist sights.
The Miyajima free pass ¥2000 includes unlimited travel on the Mt. Misen ropeway, the ferry, and Hiroshima street cars for two days, so it is a good deal even if you only plan on taking the ferry and the ropeway ropeway = ¥1800, ferry approximately ¥150 each way. It's available from the Hiroshima tourist office, and also from the conductors on the trams recommended as it will save you time.
