I have been led to understand that the goddess Asherah was worshipped as a consort of Yahweh (who eventually evolved into the modern Abrahamic God) by the ancient Israelites. How typical was this worship (i.e. was it considered "canonical"?) and how did it die out?

It's difficult to tell how widespread the worship was, but it was widespread enough that the Deuteronomistic Historian thought it important to forbid Asherah's worship. In addition, we have some archaeological evidence that worship was common enough that there were figurines produced of Asherah, and that she was more or less the queen to YHWH's king. See Dever's Did God Have a Wife?

Were there any other gods worshipped by the ancient Israelites that were erased from the tradition by monotheistic reforms, or was Yahweh the one-and-only for the most part?

Yes, probably. Baal and El were two Canaanite/Ugaritic gods that were a significant part of the Israelite pantheon. There's some scholarly disagreement here, largely depending on how accurate you think the Biblical account is. However, Psalm 72 seems a translation from Ugaritic worshipping Baal, with YHWH placed in afterward. See Mark Smith's The Ugaritic Baal Cycle for a discussion of the Psalm. Alternatively, you can read Smith's The Origins of Biblical Monotheism.

Do we know of any mythology about Yahweh that made him more "human" and physical or focused on a specific domain, more akin to pagan gods than the omnipresent and ineffable being (whose name can't even be pronounced in Judaism) that appears in Abrahamic religions today?

I can't speak as to his transformation in depiction, but if you support the Documentary Hypothesis, you see it as the sources advance (for lack of a better word) from the J source to the P/D sources. The prohibition on the pronunciation of the name is, iirc, a Rabbinic development.

What do we know about the rituals of the ancient Israelites? Did they have Shabbat or Passover or the High Holy Days? Did they pray before meals like modern Jews, or read/listen to some sort of proto-Torah? How standardized was their mythology compared to the extremely standard Torah of modern Judaism, or the Torah during the rise of rabbinic Judaism or slightly prior to it?

This is a really good question. By the Second Temple period, there were certainly some institutionalized festivals. The Qumran texts abundantly attest things like Rosh Hashanah and Yom Kippur, to the extent that the calendrical texts anathematize those who disagree with the Qumran calendar (which is solar, whereas the Temple cult uses a lunar one). Earlier than that, however, I'm not sure. Passover may be a (post) exilic development, though Shabbat is tougher to tell. The issue is that the majority of these holidays show up in the P source, which is probably exilic itself.

The Pentateuch itself was likely similar to today's Pentateuch, though potentially with a few textual variants. Primarily, the scriptures were learned by oral means, especially (at least in the 2nd Temple period) by the use of what's known as Targumim (NOT TARGUMS!), or Aramaic paraphrases of the Hebrew Bible. I imagine there was some sort of lectionary cycle, though what that is, we don't really know (I don't think there's any real evidence until the rabbinic period of it anyway).

You have to keep in mind that the Pentateuch represents elite religion and concerns, rather than the religion of the common man, who was probably illiterate.