I personally recommend the Elgato HD60 S, a phenomenal choice that works with several different gaming platforms. Capture Card - Since the Nintendo Switch doesn't support internal streaming, you'll need to purchase a capture card.
You just want to make sure that any voice recordings you do while playing come through clearly for your audience to hear. Additionally, this computer must have a USB 3.0 port to be compatible with the capture card.
While not everything on this list is vital, some of the equipment will definitely make things easier for you. You'll need equipment and software to stream your gameplay successfully. The equipment you need to stream on Twitch