1. Build a strong CS and Math background, especially since you are interested in AI, ML. Academia is the best place to do this. Look at the curriculum of top engineering schools like mit, cmu for your sophomore year and see how you can complement it with the courses you are taking. This will pay you dividends in future. You are already doing that, which is great! Try to add more structure to your execution.
2. Take advanced courses on the topics you are interested as you get to your senior year. A lot of MOOC’s have entry level courses but lack on advanced topics. You will find these scattered across university lecture videos, you already mentioned OCW.
3. For prototype projects try building things from the ground up. For e.g. Taking an Operating systems course great, build a simple filesystem from scratch. It will help you in understanding the complexity involved in production grade software and why certain design choices are made.
4. For the projects that you are passionate about deep dive into it, its great to see people talk about their projects with deep technical insight, pros and cons of design choices made etc.
5. Personally I would avoid learning every new language that comes up, focus more on programming language concepts (there is a course of Coursera on this) and learn few languages well.
6. For internships look for startups that are working on interesting ideas.
7. More than the certificates the projects what you did in those courses are more valuable.
8. Enjoy, make good friends, stay healthy and active.