Okay, I made some more improvements...
The currency information is now retrieved via the Invoice::invoicedCurrencies() method. If a client has invoices in multiple currencies, then the client will be able to select the currency from the dropdown box shown in the screenshot.
Client can select between 6 month, 12 month, or 24 month statements.
Client can select whether to open the statement in the browser window or force a PDF download.
Company name, address and telephone number are retrieved via Configure::get( "Blesta.company ).
The client will see an alert for overdue invoices on the Account Statement window, with a Pay Now button.
I think those are the main features. I'm attaching 2 screenshots. One is the Account Statement screen and the other is the rendered PDF statement.
I'll update the repo shortly (20 minutes or so). If anyone wants to test it out on their own system, any feedback is welcome, of course.