clean-code-javascript | 🛁 Clean code concepts adapted for JavaScript | Architecture library

I'm trying to call to the Google PageSpeed Insights API with mutliple input urls read from a .txt file and to output the results to a .csv.

I wrote a console app to try to fire these requests off, and then as they come back to add them to a list, and when they are all done, to write the list to the .csv file (async got a little nutty when trying to write the responses immediately to the .csv).

My code it below, and far from optimized. I come form a JavaScript background, where I usually don't use web workers or any other managed new threads, so I was trying to do the same in C#.

1. Can I run do these multiple WebRequests and write them to a collection (or output file) without using multiple threads and have them all run in parallel, not having to wait for each request to come back before handling the next one?
2. Is there a cleaner way to do this with callbacks?
3. If threads or BackgroundWorkers are needed, what's a Clean Code way of doing this?