Controlling which desktop app opens in
 

Wondering how I can make it so Mail app always opens in desktop number 2? Thanks.

That functionality is commonly referred to as "pinning." What distro/version and desktop environment are you using?

In my experience, many window managers offer the capability to "pin" an application window to a particular workspace (Fluxbox etc.). That feature is not necessarily as common with desktop environments (KDE, Gnome, XFCE, etc.), at least in my observation.

A web search for pin application linux workspace turns up a number of articles. Perhaps one of them will help.