How to customize simulations in MATLAB/Simulink?

I am working on creating a GUI where the user can open/create a model from a customized library which will contain elements/models that are totally new and different from the already existing library contents.The user can drag and drop elements into the simulink workspace and interconnect them as required to create a single line diagram(SLD). I have a few equations which would have been sufficient to solve this SLD theoretically on paper. Having these requirements how do i proceed to do my own simulations with the equations in hand? When I tried searching for a solution, the results came out either focusing on GUI creation or steps on running simulink or handling the already created codes. It would be of great help if someone could list down what steps I have to proceed in a simple way including tips as to with what language to start coding on for better handling and how to link the equations with the slx file while clicking the 'Run/Simulate' button that will be provided in the GUI window. It will sound almost like creating a custom MATLAB/Simulink environment.