QIf I evolved another follower using its evolve ability this turn, can I still evolve this follower with its own automatic ability at the start of my end phase?

AYes. Although you can only activate one evolve ability per turn, other abilities that evolve followers do not count towards this limit.

QIf I'm playing against 3 other players, and each opponent puts a follower into the cemetery from their field this turn, will that satisfy the condition of this follower's ability?

AYes. As long as a total of 3 enemy followers are put into the cemetery from the field, they can be from any opponent.

QIf I'm playing against 3 other players, and an opponent loses while this follower is on my field, does the number of times it can attack change?

AYes, it does.