quicktilo When connecting a GOS device to a computer, will any data of the computer be saved on the GOS device or vice versa?
The only 'data' that may be stored is when connecting for file transfer purposes is the device name on the host laptop, on Windows for example you can type in CMD or Powershell:
Get-ItemProperty -Path HKLM:\SYSTEM\CurrentControlSet\Enum\USBSTOR\*\* | Select FriendlyName
What's the maximum USB thumb drive size that can be connected directly to a GOS device and can it be formatted as NTFS?
As lberrymage mentioned it does have to be formatted as FAT32 and I can confirm that thumb drive wise I use 128GB one however Android is designed for portable ssd's to be connected too but just be aware that the larger the capacity and type of device it may need external power.
Can I backup the GOS device to a USB thumb drive directly from the USB-C port and restore everything in the same way to a new device?
Yes again as @lberrymage said you can go to Settings -> System -> Backup however the app currently used 'Seedvault' is considered slightly unreliable. GOS has roadmapped a replacement due to this. It is best used in conjunction with individual apps backup/restore features. Where you can you should use those to backup contacts, calendar, app settings etc.
Is activating hotspot in the GOS device safe when other android devices connect to it (can other devices take data from the GOS device) or vice versa?
Absolutely it's as secure as any other WiFi hotspot/router, it obviously broadcasts it's SSID and communication is secured using the existing WiFi WPA2 protocol.
Is there an advantage of using a different user profile rather than a work profile and how easy is it to change a user in the GOS device?
Yes and again to develop the previous response, Work Profiles were generally only desired or needed on GOS for notification purposes. GrapheneOS now offers a notification forwarding service between users which you can read about here: https://grapheneos.org/features#notification-forwarding
Is there any difference between the Google camera app and the GOS device camera?
There are but they both tend to trade blow for blow in various circumstances. The GOS Camera depends on CameraX vendor extensions which are device dependent for the full range of facilities such as Night Sight to be available. Once Google releases these for Pixels I don't see there being any difference at all or need for the latter. I use GOS Cam as my go to without issue. Some sample images: https://nitter.net/Metr0pl3x/status/1529571511056707585
When installing apps like Instagram, Snapchat or WhatsApp, which metadata or information is collected from the GOS device?
Apps only get what you give them and use that information as per their policies.
Some places to start:
We know that a computer virus targets a specific operating system, are there specific viruses if the hacker knows I'm using a GOS device?
Off topic, are you using a separate GPS device for navigation and which one do you recommend?
No, I make use of Osmand+, Organic Maps etc where possible and Google Maps in a dedicated Play Services profile where necessary.