Do performance profiling and load testing during development, as part of test routines, and before final release to ensure the application performs and scales as required. When optimizing performance, look at network throughput, CPU, and RAM requirements.
Measuring performance is important when you tune the number of requests to issue to Data API concurrently. Measure the network bandwidth being achieved over single request and the use of other resources that your application uses in processing the data. You can then identify the bottleneck resource (that is, the resource with the highest usage), and hence the number of requests that are likely to be useful. Even small number of concurrent requests (20 concurrent requests of 50-80 MB/s of desired network throughput) can saturate a 10 Gb/s network interface card (NIC). Going with too low parallelism will result in underutilized resources, with too high in resource congestion.