Your questions about disease are best answered by /u/anthropology_nerd, who is flaired in the topic.

Myths of Conquest Part Seven deals with this as part of a series structured similarly to a book by Matthew Restall.

Did the Colombian Exchange put Native American civilizations into unrecoverable decline?

Annotated Reading List (incuding the Restall book, see also the subreddit booklist)

EDIT: See also these FAQ entries about the enslavement of indigenous peoples.

/u/Snapshot has written on this topic numerous times.

Why is the European colonisation of North America seen as so morally wrong?

Why the genocide was not an accident.

Meta/historiography about Columbus Day

Dissecting a PragerU video about Columbus Day (feat. discussion of disease as genocide)

More about what % of genocide was because of disease.

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/u/Ucumu has answered How much of the Native American deaths were caused by disease and how much by the colonial powers?