Estimates of the population of North America in 1491 disagree by an order of magnitude—from 18 million, Dobyns's revised figure, to 1.8 million, calculated by Douglas H. Ubelaker, an anthropologist at the Smithsonian.

A book titled 1491 by Charles Mann goes into extreme detail about the daily lives of Americans before Europe settled. It's fascinating to see how similar their forms of diplomacy and trade to Europeans who possessed far more technology. Check it out if you wanna know more about how Native American societies were configured.

This question is going to be nearly impossible to get a definitive answer on. Russell Thornton, a professor of anthropology at the University of California, wrote a book called "American Indian Holocaust and Survival: A Population History Since 1492" (forgive me for not knowing how to use italics on Reddit). His book gives a wide range of estimates from various sources, some as low as about 150,000 and some as high as 5 million. Regardless, it is an interesting read if you are into American History before European arrival.