As is often the case, it depends on where the bottleneck(s) are. If the bottleneck is downloading the CSV file then you could start by streaming the CSV rather than downloading it and then chunking the data to SQS.
If the constraint is adding to SQS I would suggest looking at flow as a way to have configurable concurrent consumers/producers. Some of the strategies would depend on whether or not ordering of events pushed into SQS matters.
