You could try coursera. They provide free online courses offered by various universities. They are well organized and easy to access. They usually offer some materials and might require or suggest you buy a few books. I'd stick with the required to stuff to save money.
I would also try to not get carried away as it can become an addiction trying to consume as much information as possible. Do one or two courses at a time, max, depending on the amount of free time you have available.
As far as topics? Just start exploring. They have tons. But I'd suggest getting a good variety. For example, a course on Buddhism and then a course on argumentation. A course on history and then one on personal finance. Here are some of their offerings:
https://www.coursera.org/learn/leading-the-life-you-want
https://www.coursera.org/learn/science-of-meditation?
https://www.coursera.org/learn/modern-world
https://www.coursera.org/learn/the-science-of-well-being
https://www.coursera.org/learn/understanding-arguments
https://www.coursera.org/learn/philosophy