Build Website with token payment system

I need a platform developed with an internal currency built-in. It essentially a simulation game which offers users the ability to invest fictional ‘play money’ into in-game tokens that follow real-time prices through APIs. Either has any value outside the game and are only used as components and mechanisms to create the basis of the investment game. The system is expected to remain open for new additions to be added such as extra functionalities and features. It is expected to have the highest measurements of security protocols set in place to prevent information leakage, exploits or any other malicious intent. The user interface is expected to work regardless of device and browser and to have the speed of a modern web application despite having a lot of dynamic content and continuous API requests. The main priority is to ensure that the platform is built with speed, scalability, security and stability in mind. The frontend should preferably be built in React / Angular 6 / Vue.js. We require a unit-test as development commences to ensure that the platform can be maintained in the future. The backend should preferably be done in Java or C# and can either be self-hosted or hosted in the cloud, depending on what offers greater security and scalability.