Make split invoices in magento and add automatic status changes

We have a downpayment option for our customer in our Magento store. We would like magento to automatically create a split invoice, of of 30% and one of 70%. Both of the invoices should also be unpaid and should be a trigger for a orderstatus change when the invoice is set to paid. Please read the following steps how we want it to be: 1. Customer places an order with our downpayment option ‘Achteraf betalen’, which is ‘Check / Money Order’ 2. Magento creates the first invoice of 30% of the total order amount. When the invoice is created, the customer receives the invoice (with 30%) automatically with the standard invoice e-mail template (as if the customer has paid with a PSP). - The status of this first invoice should be ‘Unpaid’. 3. When the customer pays the invoice we have to be able to set the status of the invoice manually to ‘Paid’ 4. The product will be shipped by using the the ‘send’ button in the order in Magento. When the order has been shipped – Magento has to create the 2nd invoice with the remaining 70% of the total amount. The customer has to receive the invoice (with 70% of the total amount) automatically in their e-mail. - The status of this 2nd invoice should also be ‘Unpaid’. 5. When the customer has paid the remaining 70% of the order. We have to be able to set the status of the invoice automatically to paid. When we set the 2nd invoice status to paid – The order status should automatically change to ‘complete’. !!!!!! Please be aware !!!!!! – These unpaid invoices or automatic status changes should only apply when a customer has chosen the payment option ‘Achteraf betalen’ in english: ‘Check / Money Order’. In every other payment option there should be NO changes to the current settings. NOTE TO DEVELOPER: You will be developing in our staging / development website. Please note every single change or step you made and in which file you have made the changes. We will be making the changes to the live website ourselves. ----- It's a very clean Magento installation, you will receive the website after your bid -------