I'm trying to set up the REST API environment in postman, but I can't figure out what file I'm supposed to use from the NetsuiteDataLoader zip

I followed this documentation to get it working for my environment. https://docs.oracle.com/cloud/latest/netsuitecs_gs/NSTRW/NSTRW.pdf

You need to have REST Web Services feature enabled and have Admin role or role having REST Web Services permission set. Then you should see .zip file with Postman collection examples for REST Web Services available for download.