QIf my field is full, and I have 4 Natura cards on my field, can I bury them to summon this follower?

AYes, you can.

QIf I summon a Wildwood Matriarch with this follower's Fanfare ability, will the Wildwood Matriarch evolve with its Fanfare ability?

AYes, it will.

QIf I bury 4 Naterran Great Tree tokens when playing this follower, and I discard an Elf follower that costs 5 or less with a Naterran Great Tree's automatic ability, can I summon that Elf follower with this follower's Fanfare ability?

AYes. Since Naterran Great Tree's automatic ability and this follower's Fanfare ability are triggered at the same time, you can resolve them in any order. If you resolve Naterran Great Tree's automatic ability first and discard the Elf follower, you can use this follower's Fanfare ability to summon it from the cemetery.

QIf I discard this follower during my end phase because I have too many cards in my hand, do I put a Naterran Great Tree token into my EX area?

AYes, you do.