#1. It is recommended to clean up your desktop. The more cluttered your desktop is, the slower your system will become.
#2. There is no way to find a file that is already open. You should look for a type of resource monitor program. You can search for it in a program like Processor Explorer.
#3. There are methods such as setting "Always on Top" using auxiliary programs such as Powertoy.
#4. There is also a way to utilize virtual desktops, etc.