I think I'll start with an answer (or partial answer) to the first question egorjosh2 posted.
Didn't the White Council enlist the help of the elves of Lothlorian to attack Dol Gulder or am I just remembering the fact that Sauron launched 3 attacks from Dol Gulder against Lorien during the War of the Ring?
I can not answer as to an army of elves attacking, but Galadriel is on the White Council. At least she is as I understand it. And as the defacto leader of the Noldor Elves and one who has lived in the light of the Trees, I would imagine she is on the council. From there it is no real stretch to presume that the elves of Lothlorien would aid in the attack of Dol Guldor.
Go even one better. Put Haldir in the battle as well. Another repeat customer from LotR.
And further a good point on battle fatigue for putting the Dol Guldor and Five Armies in the same movie. Granted the Pelennor Fields and the Morannan were both in RotK, but the Morannan was a much smaller scale battle. I would like the assault on Dol Guldor to be bigger and better than that.
For the Hobbit break, I still want to push film one all the way to the elves of Mirkwood. I know the cliffhanger of being left in the dungeons has been floated around a bit. I still thought a better ending would be when the barrels leave port. But again, with that is the pesky too much too little balance from film to film.
For me, a small conflict for the party spider encounter, elves encounter, Beorn encounter
should not be cut by the movie break. It just hurts the flow.