Tracking Actions on Web Pages using Marketo

I know Marketo can help me track pageviews but can I track actions visitors might take on my webpage? Like the length a video may be viewed by a visitor?

Yes, you can search for old posts on video tracking in the Community and check out this demo which shows how the Munchkin API can be used for this, even with multiple videos on the page.

Additionally, can Marketo help me track engagement of my social media posts and connect that visitor to my lead database (if present) to create a comprehensive lead scoring model?

Marketo alone can't do this, but you can look at solutions like Oktopost.