Hello there,
I would advise that no one take the changes that I posted in consideration yet. There are still some problems with them. There are quite a few queries that return double products because it takes them from the products_to_categories db table as well. It is quite frustrating but I'm trusting in Him who is all wise to guide me and show me how to fix this.
If anyone has some tips or wants to join me in debugging this, you're most than welcome.

God bless you,
Iasmin