With V10, old sentry clips are over written. This was case with dashcam prior to V10.
So you need a drive large enough to save enough recorded events for as long as it will take you to view them. With the current 4 cameras, data is recorded at approx 4 * 37MB per minute clip, so around 150MB per minute, or 1.5GB per 10 minute event - sentry records around 10 minutes lead up and including an event.
I would suggest, depending on unknown number of events and how often you can check the drive, 32GB to 256GB drive with 64GB and 128GB being in the sweet spot price wise. A robust SD card in USD reader or SSD will be more reliable than a pure USB stick. But its a big subject with lots of often conflicting recommendations, so best to search other threads for what you need.