Is there an easy/efficient way to generate some high-level reports for a particular GitHub project?
e.g. lines of code committed over time, top contributors, etc
Now there are several tools that you could use (e.g. see this rather complete list: https://livablesoftware.com/tools-mine-analyze-github-git-software-data/ )
The right tool for you will also depend on you're just interested in the "git" part of the project or the "GitHub" part (i.e. stats on community activity).
I'd start by checking GrimoireLab , Apache Kibble and Sourced. They all allow you to configure and create a dashboard to display several metrics around your project