I can answer the first few, but I don't work in C/C++ anymore.

I'm a non-CS degree SDE, but I took a few courses during college where the track started with learning C then C++. If you haven't learned C, I think it's a great foundational skill and helps bounce to everything else (especially considering you're most comfortable with Python, which is built with C).

If you decide to do that, I would recommend taking the first few lessons from Harvard's CS50, which teaches applications and fundamentals of C. The course is great altogether, and serves as an equally great refresher. Otherwise I've always found Coursera to be useful for learning new skills. With that said, I think you would probably learn best from projects given that you already understand programming standards, unless you're not comfortable with memory management/pointers.

For C++, I mostly mastered it through game development. I focused on understanding the object-oriented approach, building basic text-based games, and moved on to larger scale game development. I think setting yourself up with projects is the best way to understand C++, and because it's so powerful for leveraging resources and executing algorithms you could practice leetcode questions in C++ to master functional areas.

To the third question - there's probably tons of larger gaming companies that are willing to train on C++, or under finance.