Earlier quoted context omitted.
I think your problem might be not expanding wordpress. PHP will gladly do the above through wordpress plugins and cron jobs. I built something similar and ended up going that way. The system is still running to this day. Sure, its not hip but gets the job done with miniml fuss and makes money.
You are right that PHP can do the feed checking part but I wanted to use something with easy async/concurrency out of the box (and wanted to learn Elixir instead of using Node.) One hard tech limit is that with 50k podcasts, 4million+ episodes, search definitely doesn't work well. Not just WP, but SQL itself. Hence Elasticsearch. I also plan to work on recommendations, etc. so will need probably to be exporting SQL d…
It doesn't sound like microservices are needed, just adding in the appropriate tech for the job.