So, I'm answering my own question, because I decided based on a few points. So why?
1- I have a page in which I have to manage multiple contents including a products page. What does this mean? It means that I'll display the products easily by using Symfony helpers.
2- I will also have a much easier task while creating the backend since I won't need to do anything extra (like creating .php pages for each product which would be very stupid) besides a simple CRUD to manage the contents of a webpage.
3- It will be simple to maintain the app and change on the go, with less files and in a more structured way, which is what a framework does.
So anyone having a time deciding on whether do everything in symfony or just the backend, I recommend doing everything.
Thanks to Haithem Rihane who provided nice resources.