I always thought of Dale as being larger than lake town...it rated a king & I think was the capital of the region. The whole area had been more prosperous before the dragon & even Laketown had been bigger. But both will be smaller than Minas Tirith and, I would think, Edoras.
Similarly, the main chamber under the mountain will be very large - but not as big as PJ did the Moria chamber; I can't see anything in the Hobbit out sizing places in the LOTR - or watching the movies in chronological order will lead to anti-climaxes. The approach should be different anyhow - do to the dim light, the dimensions of the chamber are only dimly guessable, so PJ does not need to try to impress us with its size. I think that PJ will try to avoid comparisons anyhow, since making the movies competitors is not to his benefit.
The troll cave would have been small (for trolls) as it was just a modest place for them to sleep during the day and stash their stuff.
Agree with others - goblin caves mostly small windy tunnels, with a few slightly larger tunnels (like where the dwarves and their ponies were brought in) and a "big cavern". Lots and lots of tangled passages though, very extensive. The goblins were unlikely to make anything bigger than they had to do or waste time on non-functional decoration, so it will have a look unlike any other underground place we see.