If you’re only intend to use Radarr you can set your NZB indexer there and your downloader.

If you plan to add more arr later like Sonarr you can use Prowlarr and just link it, and not have to configure your indexers again in Sonarr.

Honestly if you’re using nzb you’ll only really need the nzb indexer so it shouldn’t be all that hard to set up in other programmes