A *stamp shop* which is like LINE Camera for my iPhone app

I am making a iPhone photo-editing app which is like LINE Camera ([login to view URL]) Now I want to add a stamp shop in my app There should be (1) a stamp list (stamps available for purchase) and (2) a purchased stamp list Users can select a set of stamp in (1) and then user can see the stamp details users can buy it (using in-app purchase) / (some stamp sets are free so user can download them for free) and then the download begins (it can be download in background i.e. user can use the stamp shop when they downloading a stamp set) (multiple downloads can be performed at the same time) Purchased and downloaded stamp sets can be shown in (2) User can delete a stamp set but it can be downloaded again for free on stamp shop There should be a "restore in app purchase" button in stamp shop You are required to create a server to place those stamp set (you can use some free servers like Heroku) I will merge your code to my app. You need to save the stamp set in a well-organized way inside the app so the rest of my app can retrieve it. I can set up a iTunes connect account for you to set up in app purchase You need to think about how can I upload a stamp set to the server easily You can use open-source libraries in the project The appearance / buttons / graphic in the app can be bad since I will modify those graphic and UI by myself * * * * * You are required... having experience on in app purchase (please show me your previous related work) giving me the source code of the app explaining the meaning of the code to me and teach me how to maintain it (No worries - I am a iOS developer that can understand what are you talking about) explaining the settings in iTunes connect and Xcode project related to in app purchase to me I want the code are clean and scalable. Many thanks for your help!!!!!