Magento 2 Extension Development

I have a Magento 2.1.2 installation set up and need to send out one invoice at the end of the month to a customer for all his/her orders What we want to achieve is the ability to add multiple orders to one invoice. All of the orders will be for the same customer, and we should have the ability to choose from un-invoiced orders which ones to combine and send. All of the products from each order should be added to the invoice. The invoice should also reflect which order number each product is for. It would be nice if we can save generated Invoice on the backend so we have reference to it. Also all the orders should be marked as invoiced that are added to an invoice. We can create a page with an option to select a customer and a button "Create invoice" next to it. Now, within the invoice creation page, there will be a option to add uninvoiced orders one by one and then Create Invoice. So, only 1 invoice will be created against all the selected orders. After a invoice is created and sent, the corresponding orders will be marked as invoiced. The invoice will also have a status field. And, it can be marked as Paid or unpaid. So, for Customer X, I can have Orders 2,4,7 to create a invoice 1 and have Orders 1,3,5,6 to invoice 2 Everything will be in admin panel and no changes are required on frontend. Need this in 3 days.