How to setup Analytics for SaaS

My new SaaS is data driven and analytics based. I'm wondering what options are available for setting up an analytics stack.

Requirements

1. Should collect the events from each tenant through REST api's
2. Provide each tenant an option to view the results (in the form of dashboards)

This is the first time i'm working on an Analytics product so would request the community to share their views. I have the following questions to get started.

1. Are there any Open Source options?
2. Are there any plug & play options (free/paid) to integrate in my SaaS product?
3. What tech stack is quick to get started and scalable? (I'm JS/TS guy)

Thanks!