Hello,
I have developed 2 Xamarin forms apps similar to your required application
I used Sqlite to save data locally on mobile
also i have solid experience in Asp.net web API (if not ready)
Relevant Skills and Experience
Android, C# Programming, iPhone, Mobile App Development, Xamarin Forms, Asp.net , MVC, MVVM, SQL Server, Sqlite, WPF, XAML
Proposed Milestones
$100 USD - Selecting Style & Login and get data saved localy
$200 USD - In orders
$100 USD - Out orders
$100 USD - Finalize