Use a single shortcut to activate an app (might running in other spaces) in the current space
I only have a partial answer that solves following question: How to assign a single shortcut to activate an app?

This solution will:


start the app when it is not running
when it is running, bring it to the foreground, meaning that the focus will be set to this app.


This can be achieved without a third party application.


Open Automator and select Quick Action (might be called Service in version of macOS earlier than Mojave)
In the new workflow, search for the action Launch application by searching for it in the name searchbox.
Double tap Launch application, which will be added to workflow pane. 
Select your application from the dropdown list. By default only applications in /Applications will be selected, so choose other... if needed.
Save the workflow. Name it something sensible like Open MyApp.
Open System Preferences > Keyboard. Click the Shortcuts tab and select Services from the left hand pane.
Under General in the right hand pane, you will find your freshly created workflow. Assign a keyboard shortcut there. 


Hope this helps.

Tested on Catalina 10.15.4.