I'm thinking of asking my friends to help me get revenge on my ex
What makes you want to get revenge on him?
He was a terrible scumbag when I was in a relationship with him.
I'm happy for you that you have friends willing to go to such lengths to help you.  That being said, seeking revenge is usually unhealthy and a bad idea.  I'd say let the past be the past now that you two are no longer together.
I want him to know what it feels like to be alone.
Trust me, living your best life and being happy is the greatest revenge you can get. Focus on yourself and leave your ex in the past.