I know that in folder config are file called core.php which I can configure application options as a debug mode, session, cache etc. 

But I want do configure file for my application. I want for example configure how many post can be displayed in main page, thubnails size etc.

I think that the best place in config folder but where and when parse thos file in application (bootstrap, AppController another mechanism ?) and what is the best extension .ini or PHP array (for performance reason too). What is the best practice to do this ?