Indeed he is Leewerrey - at that period of his career he'd fallen back on his earlier specialism of raising the dead!
The 2 extra story arcs, especially Thorin's father and grandfather's plot, are mostly discussed in the less readable books from the 12 volume History of Middle Earth (HOME) which is basically Christopher Tolkien's reassembling of his father's copious notes and revisions of early manuscripts for the 'proper' books, that were already in print or being worked on before Tolkien Snr died. The Sil was published after Tolkien passed on of course, but a lot of it had been written by then in various editions that Christopher Tolkien and Guy Gavriel Kay pulled from his archive material. HOME includes some work that had made it into print in Lost Tales or Unfinished Tales, but not necessarily as Tolkien had passed it for publication, as he was constantly revising things whilst trying to get the Silmarillion prepared for the printers, so some it was 'out there' but more detail (some very obscure and frankly not too exciting) stayed in the notes until Christopher T really got down to archiving it all.
More specific spoilers
The fact that Tolkien hadn't really got much published on those plotlines doesn't mean that there's not much material to use because with him there always is, but to some extent you have to know where to look, because The Hobbit is, of all the Middle Earth books a stand alone novel almost. Although the LotR was mostly written around it, it doesn't actually link up too well with the Silmarillion at all, but the material from the Peoples of Middle Earth (last of the HOME books) does carry the sketch of Thror and Thrain's adventures after the fall of Erebor/the Lonely Mountain, and how Gandalf came to retrieve the map and the key that Thorin brings to the party at Bilbo's house, so there is some narrative for PJ and Phippa Boyens to adapt or elaborate on there.
The siege of Dol Guldur is referred to LotR in passing as the start of Saruman's treachery, but is tenuous within the canon as Tolkien didn't write up too much about it except to say that Elrond and Celeborn (Galadriel's husband) met with Gandalf and Radagast at Rhosgobel and drove the Necromancer out of the stronghold, but that he left several of the Nazgul behind under the leadership of Khamal (the only named Nazgul). In fact some Tolkien academics can argue quite successfully that he never actually said where Rhosgobel was in Mirkwood, but it's placed near the Old Forest Road (that eventually leads to the Carrock) in the map in the LotR, which does work in with where Gandalf would have left Bilbo and the Dwarves to go by the 'ill-tended' forest path that goes through the more north-westerly section of Mirkwood and passes the enchanted river and, of course, the stronghold of Thranduil, where he ruled a small part in the north-east of the great forest.
Celeborn was one of the senior Sindarin Lords and close kin to Thranduil and his son Legolas and they all were effectively vassals of Elrond through his mother's line of descent from the Sindarin High King, Thingol, Lord of Doriath and Overlord of Beleriand. Galadriel, although a big hitter in the White Council as the ranking noble of the Noldor (although technically Elrond outranked her through his paternal grandmother's line), also had a crucial tactical role to play in planning the siege, but that's probably where the ME canon nazis are going to be squealing over most, since Thranduil's people loathed the Noldor and in fact were barely on talking terms, even with Celeborn, after the Last Alliance at the end of the Second Age and the first fall of Mordor.
As the 3 elven ring-wielders Gandalf, Galadriel and Elrond's role in the siege would have been the lynchpins of the White Council's tactics (although those rings couldn't be used for offense or war), but Tolkien never actually fleshed out the details except to say that Saruman barely played any part except to give some minimal advice and that Radagast and Celeborn also took part so, from that there's not a lot to suggest a pitched blood and gore battle took place, but I'm sure that PJ will manage to get around that a little bit, as the Necromancer would have brought the 9 ringwraiths into the equation.
The big 'traditional' battle will be the Battle of the Five Armies of course and that most definitely will be the spectacular finale so I think with the fun in Mirkwood as per the book there ought
to be enough material to pad out 2 more films, but the die-hard purists won't like it...
I'm really looking forward to parts 2 & 3 and, like you enjoyed the LotR Trilogy, even most of the bits where liberties were taken with the book so the ladies could have a bit more to do.
I'm hoping that we might finally get to see the ultimate elven warrior Glorfindel in action at Dol Guldur at least, as we know he lived in Rivendell with Elrond and had already fought the Witchking of Angmar (chief nazgul) - he's a balrog-slayer so would be well worth watching prodding some orc-buttock! He got his bit in the LotR axed in favour of Arwen getting Frodo across the river Bruinen to safety