Build an Andoid app + Web version, Long term project

I need to build a PO creating app that can be shared in-app, whatsapp or email. Signin through gmail, fb etc. App allows consolidation of all orders placed for buyers and all orders received by seller. It will also have agent module, agent can place order on behalf of customer. Further, PO generation must be customisable (addition of new fields). PO may be revised by supplier and sent back to buyer for approval. Need to see a report of all POs - by key word search, supplier search, buyer search, agent search, product search. App must allow saving product templates. App must enable saving product pictures. Please mention in your proposal - what is your area of expertise? front end or back end? What technology do you plan to use? Have you built a similar app?