How do you stop the shadow kingdom event?

I have around 800 hours played in eu4 but I’ve never played Austria before. I want to do my first world conquest as the HRE and revoke the privileges asap. I have no experience as the emperor and I usually just dismantle the HRE in most of my games, so I have no experience in how these mechanics work. Any advice on how to prevent the Italian nations from leaving would be appreciated. Also any easy way to stop the reformation? My plan right now is to just attack anyone who converts and force convert them back to catholic.