Hello,
I have seen your requirements carefully and as per your request will make the windows app for your already developed Android App and deliver it on time line.
Approach for scope of project : I will make the design samples and send it to you for approval once your approve the design material will start working on the development part. I have developed more than 200+ apps on play and Apple stores you may check portfolio i have experienced in similar apps development.
Web back-end APIs : I will develop the web admin from where you can control everything using the Web APIs linking with the mobile apps.
Please discuss about the project in details so we can move on.
Looking forward to hear from you soon.
Thanks ,
Julian