The .exb file is a copy of your Evernote database maintained on your PC
The master version is stored on the Evernote servers
.enex files are exported Evernote data; a common backup method
This is the data you're importing
>>And I should always backup the Database folder, right?
Backing up the .exb file is an alternate backup method
>>And suppose I format the PC
You can use the backed up .exb file, or let Evernote rebuild the database from the server
This is a mainly user-supported forum, so you're unlikely to get an employee responding directly to your post.
To answer your main query - as @DTLow confirmed, all your data is stored in the EXB file. The other files in the databases folder are things like thumbnails and logs. To be able to restore your offline notebooks the best option is to copy the existing folder somewhere safe. To restore your database, or move it to a new (Windows) device
install a new 'blank' version of E