Create a configuration window for my add on I'm making an add-on that is supposed to take in a lot of user-decided configurations . I know I can create panels and stuff, but I'd prefer to create a configuration window that pops up and fills the entire screen, since there are too many options to select, and I also have to show some image thumbnails.

This new window can have all my configuration options laid out in any way I want, and can take any size, and has a close button. It can be opened using some hotkey or button when the user wants to use my add on. 

Is something like this possible?
Add-ons can have their own user preferences.
https://docs.blender.org/api/current/bpy.types.AddonPreferences.html
This doesn't fill the entire window, but this is the intended way for your add-on to be configured.