Indicate and justify the type of methodology that would be used to implement the below proposed system.
Proposed System: Paypal users should be able to use instant bank transfer as a frequent and permanent payment option when purchasing online, as well as to instantly withdraw and add funs from an to their account. A system must be developed similar to like the present instant bank transfer system for PayPal, but with some innovations, flexibility, and customization. Clearly enumerate and discuss the reasons for selecting your chosen methodology.