Regarding orchestration from the era, a book was written around that time (or slightly after) called "Orchestration for the Theater" by Francis M. Collinson (London: John Lane The Bodley Head, no date found). Needless to say, it's out of print, but you might keep an eye out for it in used book store or web searches.
It quotes liberally from the arrangements of Orellana and Robert Russell Bennett.
I was reminded of it by William's mention of five violins. The book discusses how to score for small, changeable string sections, so that, when your budget for the performance is progressively cut, or players on a bender don't make it that night, the string sound is minimally affected. They didn't think in terms of firsts and seconds, really. Violins were often scored on three staves, A, B, and C. Six or seven violins was a common total.
The author is careful to avoid two violins on any clearly audible part. One, he says, is solo and melodic; three is an ensemble. He considers two best hidden in harmonic support. Debatable, perhaps, but I do think it was common practice then.
And they often doubled instruments, almost as much of a stop-gap for bad playing or a safeguard against missing players. Shades of junior high band. But the practice of doubling tends to define that sonority (as mentioned by others here).
Though this is not its intent, the book becomes a default overview of the earliest film music because such pit bands were a. what they knew, and b. what they could afford.
And (I'm guessing), it was just before composers were learning how microphones and rudimentary mixing were changing the acoustic rules in which they'd been trained. In fact, the author alludes disparagingly to the impact technology was beginning to have on theater orchestration (I think his perspective was late thirties, early forties, in London).
By the way, I know that Gilbert and Sullivan's Mikado is available in a Dover score, and other operettas are probably offered too. What strikes you immediately is the utter simplicity of orchestration -- which is likely the sound you're looking for. In this sense, the term "film music" betrays us on many levels. Chamber strings is absolutely what you want.
