For (1), not currently. You could call Get Events for the Subscribed to List metric (using a metric_id filter), and optional time frames, and then fetch the event property with the list ID and generate your own growth data.
You could also create a segment of all profiles in a given list and then going forward, use the API to track membership in that segment. But that wouldn’t work for past profiles who’d joined the list.
For (2), yes, use the reporting API: https://developers.klaviyo.com/en/reference/reporting_api_overview#flows