What is the correct way to send a node list to the REST API?
Solution 1: Custom Endpoint

Unfortunately, entities are expected to be created one by one when using RESTful web services. You can create your own web service endpoint by writing a custom module and there, you can create support for creating multiple nodes with a single request. However, you'll still have to use batches of say, 50 nodes per request for things to work smoothly. This is more of a push import.

You might also want to try the jsonapi module to see if supports importing multiple operations in a single request.

Solution 2: Migrate API

Have you considered Drupal's migrate API instead? With migrate, you can import nodes from a remote XML / JSON document with a simple drush command which you can setup as a part of cron on your server. You can update existing items and create non-existing items. Migrate will also create nodes one by one, but it will be much faster than REST requests because it will not involve 1 HTTP request per node. This is more of a pull import.