How to use controllers and model code of theme used as plugin in Cakephp 3

I am new to cakephp, and started working on ecommerce site. Created plugin for theme Admin panel, the structure of admin panel theme plugin is as follows:


|_ config
|_ src
|_ Controller

Now the confusion is where should i put my controller and model for AdminPanel theme, in the main src folder if i put all my code it will be mixed with my other application code, and the second thing i want to create other theme for my main application, what is the correct way to use multiple plugin and the most important where to put the coding part (i.e. controllers and models) if i want to use two theme.