Its a scam
Many such reports of similar email threats, along similar lines not to broadcast your browsing habits 'keeping your guilty secret,' etc. etc. As for having access to your webcam, even if he did (which I doubt) do what many others do use a post-it note to obscure it. I have done this on my win10 laptop, even though I don't expect to be hacked.
Intrusions into your computer have to get established and I do believe avast Web Shield should either prevent this from happening at website level. The receipt of an email isn't enough to do this unless you A) open it and B) click any of the links on the suspect email. I also use MailWasher Pro that allows me to view a small part of an email (in plain text) to determine if I will even download the email.
Plus the Behaviour Shield should also protect against Intrusion (Suspicious Program Behaviour).
The thing that makes me mad is this prat effectively expects you to trust him if you did pay (and I never would), you're home free. You are more likely to have your email address sold to other scammers.
All that said, always have a robust Backup and Recovery Strategy. I use hard drive imaging software for this to backup Drives, Partitions, etc. and I run it weekly and save the backups to an external drive, I keep the last 6 backups.
