What do I need to know before doorbell shopping?

Our old chime doorbell has failed. Time to get a new one.

Considering some kind of security installation while I’m at it.

I need some basic advice. What do I need to know before I shop?

1. Do doorbell and camera come as one unit?
2. Are they DIY-installable? (by my son, not by me)
3. What is a good, down-to-earth brand and model that’ll do the job without a lot of frills?
4. I want to hear the chime before I buy. Can I do that online?
5. Best to go to my nearest Home Depot, or can I do okay on Amazon?
6. What is a ballpark price range?

Thank you very much.