Mobile application "catalogue of postage stamps"

Dear colleagues!
You need to create a mobile application that will sell subscriptions to postage stamp catalogs.
All the nuances are described in the attached file.
Term of execution 2-3 months.
Payment is most likely through a secure transaction.
Ready to discuss!
To save time, please answer the following questions:
How will the project be implemented – will the application be native or cross-platform?
How (by what software) will the server part, subscription, adminka, database, security be implemented?
What is the time frame for implementation,
Stages?
Prices?
Thank you!