Signature capture on Xero delivery notes

IOS App requires writing that integrates with Xero accounts software and usable on Iphone and IPad. I visit customers sites and service equipment using parts stocked my van. I need to either create an estimate in Xero that opens in the app or create a document in the app using customer and product data from Xero. The document needs to be able to be opened on the device as a delivery note or worksheet (without prices) or a quote (with prices). Signatures, on the device I need to be able to capture two signatures on the document, one from the person that created the document and one from the customer confirming receipt of the goods on the delivery note. Email, I need to send the document as a PDF to the customer from the app. Invoicing, I then need to be able to update this into an invoice in Xero from the app and attach the signed document to it. Photos, It would help if we could attatch photos. I currently use a free app called Joist which works quite well but does not integrate with Xero. If you are interested in the project please download joist to see what is basically required. Please ask questions. Important, how the app is going to be supported in the future, what can go wrong, how is the app stored, I dont know if it requires a IP server? This project will require knowledge of API application. Thanks for looking.