Why are Buddhas always Indian, male and human? Dipankara, Siddhartha Gotama, Maithreya to name a few (of the 28 named in the Buddhavamsa) - it feels a bit like a Hollywood plot where it's always only an all American hero that fights off the alien invasion of planet Earth.

Given that the dharma is universal why isn't a Buddha a deva or a Pacific islander or a woman?

Why is it also always only one person and not like say a united nations of Buddhas?
The question has two parts. Why only one Buddha? This is only in the Theravāda. In other Buddhist schools two, five, or up to millions of Buddhas can be seen. Two in the White Lotus, Five in the five Buddha Maṇḍala (featuring Vairocana Tathāgata, Akṣobhya Tathāgata, Ratnasambhava Tathāgata, Amitābha Tathāgata, and Amoghasiddhi Tathāgata), and an infinite number in the Avatamsaka Sūtra. Most non-Theravādin schools accept the existence of multiple Buddhists. 



The second part is why ethnically North Indian? Artists in different countries tend to depict the Buddha as having features similar to their own ethnic group, and besides have nationally distinctive styles, so one can usually tell say a Khmer Buddha from a Chinese, or a Tibetan. Many of the Buddhist artists (the image is by my colleague Dharmacārī Āloka) I know paint the Buddha as similar to themselves - since most of the artists I know are English or Kiwis, their paintings tend to look Anglo-Saxon. But there's nothing to stop, say someone of African descent portraying the Buddha as African. 

And of course there is some cross over. So Khmer artists tend to portray solitary Buddhas but with Khmer features, whereas Tibetans portray many Buddhas with Tibetan features. For some artists it makes sense to portray Gautama Buddha as an Indian because it seems more historically authentic, though of course we do not know the ethnic identity of Buddha - it's possible the Śākyas originally came from Iran for example.