tor – Would a VPN prevent hackers from accessing my network if it was already damaged?

Hypothetically, if someone had illegally accessed your network, wireless or the like. If you set up a VPN, would it prevent the attacker from seeing everything you would do or would he have pre-access to the network before configuring the VPN?

In addition, if I set up a VPN, what protections does it give me to prevent people from accessing my email, what I do online, the ability to communicate through our phones, and so on. ?

As additional security, is the general consensus to use a browser or Tor configuration (you do not know what the technical terms are) and to use a VPN?

Basically, I just want to take exaggerated measures to protect my network and any device that uses it too.