How to test a distributed systems project?

I have made a toy distributed systems project which is a service that exposes multiple CRUD APIs. I am using some AWS component (Dynamo, SQS etc.) for every part of the service. Question 1: How do I test the scalability and availability of my system? I want to see how much load it can handle and how well does it scale from 10 users to a million users. Are there tools or test environments available? To simulate real world problems like servers go down or sudden increase in user traffic on a service? What I ideally want to learn is, if this API is used in a real world setting, and a startup starts with 10 users and grows to a million users, I need to learn how to scale the system (horizontal vs vertical) to keep up the availability of the system (reduce crashes or 500 errors). I have limited money to experiment on this and can spare $50 a month max. (Working within the free tier right now that AWS provides.) Question 2: Is this the right way to learn distributed systems architecture? I prefer a practical approach and not a theoretical one.