/u/iphikrates and /u/toldinstone both have posts devoted to the source issue for Alexander the Great that you might find interesting:

/u/iphikrates https://www.reddit.com/r/AskHistorians/comments/9vh3eg/aristotle_died_in_322_bc_one_year_after_the_death/e9d3z8m https://www.reddit.com/r/AskHistorians/comments/4njetx/what_contemporary_evidence_do_we_have_for/

/u/toldinstone https://www.reddit.com/r/AskHistorians/comments/aa4un6/ive_heard_that_arrian_is_considered_the_most/