“Many subsects” is kind of misleading. While there are several specific subsects that propound particular dogmas (Vaishnavism, for example, and all the personality cults), most Hindus do not ascribe to any particular sect and consider themselves merely to be “Hindus” without further specificity. It is true that specific practices vary widely from place-to-place, family-to-family, and individual-to-individual, but to most Hindus, it is simply all “Hinduism.” There is no rivalry between vegetarian Vaishnavites (Vishnu/Krishna worshippers) and meat-eating Shaivites (Shiva worshippers), for example.
Except for the specific practices of certain wandering mendicants, labels like “Shaivite” or “Shaktist” (worshippers of the Goddess of Power) act more descriptively than as designators of particular sects. That is, you can look at a specific religious practice and say “that’s Shaivite” or that’s Shaktism," but very rarely will anyone say something like “I do this and not that because I’m a Shaktist and not a Vaishnavite.” And, really, most people will engage in a variety of practices.
It would hard to be a literalist in some sense, because Hinduism has no basic text that is considered the divine word that propounds Hindu dogma.
Yes and no. Very generally speaking, less educated people tend to take things more literally and more educated people tend to take things more as metaphor. But these don’t divide Hinduism into sects. They’re all just Hindus.
Because, practically speaking, there is not very much theology in Hinduism. Except for belief in reincarnation and in universalism (i.e., all beliefs are valid), there is not much in common among Hindus. There are no tests of belief that one must pass in order to be a Hindu. You must simply be born to a Hindu family. (Many Hindus don’t believe that you can convert to Hinduism, but most will gladly accept anyone who wants to join in.) Hindus also do not hesitate to take part in non-Hindu religious practices. It makes it frustrating for missionaries, for example, when the majority of middle-class children are enrolled in Catholic schools and freely take part in Christian-centered activities without ever feeling that they are in conflict with their Hinduism.
A central idea of Hindu philosophy is that god is everyone and everything. Note that is. It’s not that god is everywhere. It’s that everyone and everything is literally god. So anyone or anything can and are worshipped, including the prophets and deities of other religions, living holy men, little girls, trees, rocks, mounds of dirt. They’re all god, so they can all be worshipped.
Think about the Hindu greeting – palms together – it’s a prayer. You are literally praying to the other person because he or she is god.
I believe Murugan is the equivalent of Kartikeya, the god of war. But these things are pretty fluid and hard to pin down.
The most important god in southern India is, I think, Venkateshwara, who is seen as a parallel of Vishnu (who encompasses Rama and Krishna).