Oh, I know you're not joking about that. I have...concerns...about the 450 year long Season 4 we have planned. And the Execs continue to joke about 'Of Beleriand and its Realms' being an uneventful stretch of text.
Things that have to happen after Season 3 (which ends with the rising of the sun) and the beginning of the Beren/Luthien story:
Fingon rescues Maedhros
Maedhros acknowledges Fingolfin as High King
Yes, yes, the Noldor establish some realms...
Romance/Marriage of Galadriel and Celeborn (and anyone else we need to have kids before the wars)
Feast of Reuniting
Dagor Aglareb
Thingol finds out about the Kinslaying
Daeron's interest in Luthien and her blowing him off
Finrod and Turgon have their dreams from Ulmo to build secret fortresses - Nargothrond and Gondolin
Oh hi there Glaurung
Caranthir meets dwarves
Finrod meets Men
Aredhel leaves Gondolin, meets Eol, has Maeglin, and the two of them go back to Gondolin
Romance/Non-marriage of Aegnor and Andreth
Haleth's battle with the orcs - she meets Caranthir; leads her people through Nan Dungortheb
Hador in Dor Lomin
Battle of Sudden Flame
Barahir saves Finrod in the retreat
Death of Fingolfin
Here's the snippet from the Annals that covers First Age 5-455:
5 Fingon rescues Maedhros and the Noldor are reunited.
7 Sons of Fëanor leave Mithrim.
20 Fingolfin holds the Feast of Reuniting
52 Finrod begins to build Nargothrond
53 Turgon discovers the site of Gondolin
60 Dagor Aglareb. Morgoth invades Beleriand and is defeated.
64 Turgon begins the building of Gondolin
67 Thingol bans Quenya from Doriath
102 Nargothrond is completed
116 Gondolin is completed
150 Caranthir makes contact with the Dwarves
155 Morgoth attempts to attack Hithlum and is driven off
260 Glaurung invades Ard-galen and is repelled by Fingon (
2)
310 Finrod meets Bëor (
7)
312 Haladin enter Beleriand
313 People of Marach enter Beleriand
316 Aredhel encounters Eöl
320 Birth of Maeglin
355 Death of Bëor
369 Bereg leads some of the Edain back to the East
375 Haleth becomes chief of the Haladin
376 Haladin settle in Estolad
390 Haladin leave Estolad
400 Aredhel and Maeglin ride to Gondolin. Deaths of Aredhel and Eöl.
410 Boromir of the House of Bëor becomes lord of Ladros in Dorthonion
416 Fingolfin gives Dorlómin to Hador
420 Death of Haleth
432 Birth of Beren
441 Birth of Húrin
443 Birth of Morwen
444 Birth of Huor
455 Dagor Bragollach. Deaths of Angrod and Aegnor.
456 Death of Fingolfin