Can you request multiple securities in one go?

Yes can add an array of InstrumentIdentifier objects to your Instrument List.

eg, var result2 = extractionsContext.InstrumentListOperations.AppendIdentifiers(instrumentList, array_stage, false)

Then schedule an extraction using this list. This will allow up to 75,000 instruments to be extracted. Any more and you will need to do multiple extractions within a loop