I've begun looking for resources to learn deep learning / machine learning with the hopes of getting a job in the field within the next few years, what other fields of math would you recommend brushing up on before beginning to use some of the online sources specified in your post?
I absolutely do this as well and I'm not ashamed to admit that I've been able to come up with some solutions by smoking a bit of weed and just thinking about work. It can really open your mind if you can think clearly enough.