Note: I build and maintain such systems for a living.

There's a lot of context that's missing from your post, some questions that can help us guide you in the right direction:

1) Can your website call out to external services, or are you limited to operating behind a company network?

2) Is this more of an ad-hoc analysis or do you want to invest in a framework to be able to track such metrics systematically over time?

3) How important is data accuracy? Adblock can easily mess with client-side metrics.

4) How real-time do metrics need to be? The big trade-off here is speed vs accuracy.

5) How long do you intend to keep this data? This is a pretty big concern with regards to privacy and storage costs.

If you'd rather not share some of these answers on a public forum, feel free to shoot me an email.