Hi,
Every chapter has an overlaying story, however depending on the route you pick you interact with different characters in different ways. That will lead to different things happening, so while a chapter may be focused around John, if you are on Mike's route it will play out differently and you will still only be pursuing Mike, and vice-versa.
To clarify, if you are on Mike's route, the only character the main character will pursue romantically is Mike.
As for the rest, thank you for your kind words and I wish you the best of luck in your creative efforts. If you plan on using ren'py, don't hesitate to reach out if you have any questions and I'll do my best to respond.
/Grunt