Easiest way to do it imo is to buy a PiAware kit from FlightAware, which has all the hardware you need. You'll start feeding to FlightAware right away, but they honor censoring requests, so you can then configure it to also feed to ADS-B Exchange.
https://files.mastodon.tonywebster.com/media_attachments/files/000/164/433/original/01b96c979d2b052e.jpeg