Welcome
The easy question first. No, Gramps does not store the raw media files within Gramps. The only thing saved is the path name to the file. You can create a backup file with the raw media files. This file can become quite large. I just use the backup created on exit which does not have this option. Just remember to make your own backup of your media files.
Gramps uses a Base Relative Media Path (menu >> Edit >> Preferences) on the General tab. I am on Win10 and I have mine set to c:\user\public\genealogy\Media If I want to move the media to a new location, all I have to change is this path.
On adding the media, there will be a checkbox Convert to a Relative Path. Gramps will strip out the path information set in Preferences leaving just the file name and any folder structure within the media folder.
You can drag-n-drop a selection of the raw files and drop them into the Media view list. A Gramps record for each file will be created. You would still need to make any adjustments to the record’s Title and Date fields. And of course the records will not be added to the appropriate Gallery tab to be linked within Gramps.
You can do the same drag-n-drop of a media file into the appropriate Gallery tab. You can d-n-d Aunt Mary’s photo into her Gallery tab, The media record will be created and linked to her. and it will be easier to edit the Title and Date fields.
One of the background information set in Gramps when the record is created is the file’s checksum. Using the Media Verify tool you can move and rename files and the tool will find the files again based upon the checksum.
An example. I broke my one Census folder into separate folders based upon year and country. I also renamed files. I no longer had to name a file by year now that they were in the appropriate year folder. Running the Verify tool Gramps found all those files and made the adjustment to the record’s path field. If you make an edit to the raw media file, crop, resize, etc, the checksums will no longer agree. The Verify tool’s Generate option will reset all checksums. So before making any move or renaming, make sure to run the Generate option so Verify can find them again. Running the Check and Repair tool will also reset all checksums.
If you have a photo with more than one person, you can share the photo with all the individuals and select just the relevant person in the photo. I will leave you to explore this option
How to create image reference regions
I will offer no advice about how to organize the raw files in the media folder. There are as many ways as there are users. That can be its own discussion.