Terrible situation to be in but it is rare for anyone to harbour this sort of anger for 8 years. I think if he bumped in to you in the street he'd be embarrassed and keep out of your way, but that won't give you peace of mind.
I have a Ring doorbell and it is excellent. The images go straight to the cloud so even if it is vandalised the footage is safe. I get a quick reaction on my devices so that I can who is at the door before they even ring the doorbell. I would install a camera at the back of the property, too.
I think strong bolts top and bottom of external doors are better than a chain - if you have the camera you won't need to open the door to know who is there.
Hopefully you'll feel less stressed after you've been living in the house for a couple of weeks.