I want to build a ASP.NET MVC SAS based application

Question

I want to hire some freelancer to make a web and mobile application my application scope is very broader it is having some real time financial transactions , also it contain sensitive date I have asked my developer to use ASP.NET MVC with Angular and web api , so what security constraints i should ask them to implement like my application will contain bank account detail and lot of other sensitive date , Secondly i want the owner of the code just belongs to me how can i achieve that too.

 

Thanks for advice