I'm not sure what you're trying to build, but by the end of the second course, you should be able to create a customer service chatbot that is equivalent to what others have built. If you're interested in building/fine-tuning an LLM, that's totally beyond my knowledge.
MIT posts their AI/ML Degree requirements online, as well as the courses, for free. Shouldn't take you more than a year to finish it and start reading research papers.
I think I'd be more interested in exploring how to build new things if so.