Is there a way to sort the apps by usage frequncy?
I haven't seen any Spotlight metadata that counts the number an app is launched, you can, however, use the Date Last opened as a reference.

Open your /Applications folder and right click on the sort bar (where it says name, date modified, Size, etc.) and select Date Last Opened. Click on that to sort by that column and that's as close as you can get.



If you're feeling fancy, you can create a smart folder that only shows the apps that you've opened in the last  number of days, weeks, etc. :)