We have a customer self-service portal that is white-labeled, so clients can add their own logos. Clients can create their own design if they prefer, which we can integrate with information from the back office (invoices, usage, balance, etc.).
Yes we can, at the General Ledger Level, as well as at the transaction level.
The most common method is using CSV files. In more complex cases, we can write scripts, should any additional data sorting functionality be needed.