We have about 50,000 leads and wanted to pull them through a nightly processes using REST API. Can I use /rest/v1/leads.json.. if so what filter types and value I can use. Please suggest.
You could look at the Bulk Extract API for Leads. Once you have the initial leads pulled, you can pull just updates every night via the Bulk Extract. The initial pull isn't straightforward either using the regular API that you specify or the bulk extract, you'll have to do some kind of loop with either.