It behaves like 2 computers. I have mine set up to change my input from 3 monitors to 2 monitors when the VM starts with qemuhooks by running a xrandr script. You can position the 2 monitors virtually wherever you want. qemuhooks executes another script when it shuts down to switch back to 3 monitors. (Arandr is a great gui to set up the monitors the way you like them and then save the setup as a script)

I have 2 mice and 2 keyboards. Gaming one is just the left half of a split keyboard. The gaming mouse and gaming keyboard get passed through automatically on VM startup.

You can use one kb and mouse on both the host and guest but need to manage switching back and forth with keybinds. There are probably other solutions that I am not aware of maybe ones that let you move the mouse in and out of the virtual machine.

I really like this setup though since I can have a web browser, discord, music etc open on the host and can just switch kb/mouse to control them and don't need to worry about switching the input back and forth or cycling focus (alt tab etc.) the way i would if I was not using a virtual machine.

If I want to use the mic in game and also on discord I pass the mic through to the guest and just run discord in there.

I liked the setup so much that I installed a Linux VM. Eventually everything I was playing worked on Linux and I didn't need windows anymore so I got rid of it but still use the passthrough.

Enable logging in your samba config and check the log for clues.