B2’s first 10G of storage is free, and the first 1G of download per day is free after that. Afterwards they charge $0.01/G.
When creating your “Application Keys” keep in mind that the “Application Key ID” is the “Access Key” and the “Application Key” is the “Secret”.
While the specific origins you want to support are up to you, make sure the API for CORS support is set to either “S3” or “Both”.
Expiration of old files on B2
You can have B2 delete old video files every day to keep your storage low by simply changing the Lifecycle Settings in the B2 dashboard.