3 . Is it possible to create Unity 3D application to display on multiple/tiled screens? For example can we set screen resolution to 3840x1200 (which means two monitors with 1920x1200 resolution side by side)?
Yes. You could create your own screen settings menu and use Screen.SetResolution.
There are options to limit what aspect ratios your game will support (ie. 4:3, 10:9, etc.) in the Player options.
Yes, but it’s a bit of a hack and is not supported by all graphics cards. Assuming your graphics card supports multi-screen spanning, what you need to do is set Screen.SetResolution to 3840x1200 (or do it in the Player settings). Some graphics cards will support doing this in full screen mode, while others will only support it when the game is in a window.
Do a search here for multi-monitor support and you should find a couple threads on the subject that will give you more info.