Here is the link to part one of this series, you might want to start there.
Based on the before stated principles and requirements for the prototyping platform I came up with the following architecture:
On the left, you see the web server where the HTML of the Prototyping tool will be stored. On the right, the different hardware components (sensors and actuators, e.g. buttons, rotary encoders, LEDs) are connected to ESP8266 microcontrollers. In broad terms, ESPs are similar to Arduinos but also offer WiFi connectivity for a low price. In between sits a server to broker and translate the information coming from both sides.