Musical U: This website is headed by a great music educator named Christopher Sutton. It's an outstanding resource for all things related to Music Theory, including ear training, scales, chord building, the Circle of Fifths, and more! It's subscription based, but there's tons of free resources!
Recommended 5-String Banjo Resources
Banjo Ben: Ben Clark has built a music teaching empire focused on Bluegrass music. There's tons of Tablature of bluegrass songs and fiddle tunes, for Five-String Banjo, Guitar, and the Mandolin. Subscription based, but there's tons of free resources! I'm a Gold Pick Member. :-)