Ask HN: How do you monitor usage of your websites?

I am about to go live with a website and want to be able to easily monitor key areas like

- general web traffic / page visits

- number of registered users

- DB space by registered user

- file system space by registered user (their uploads)

What sort of tools helped you when you started out, or did roll your own solution?

The main reason for monitoring is to - work out which features are being used and not being used - get a bit of notification if I need to increase disk space on my host.

I'm using pythonanywhere and they have a nice interface for web traffic, but would like a bit more detail.