Write some software

I need you to develop some software for me. I would like this software to be developed for Windows . We ar online retailer ( Ebay /amazon , magento,wowcher,groupon,shopify) , we also do wholesale to our local customers and unwide B2B, also we do drop shipment for our wholesale customers , we want to get invoices created automatically for our wholesale B2B customers and get our inventory correct with our normal retails orders aswell ,