Even though you specifically say you are willing to go full blown PhD and are interested in digging deep on algorithms etc. I strongly recommend working through

Even though you specifically say you are willing to go full blown PhD and are interested in digging deep on algorithms etc. I strongly recommend working through "Practical Deep Learning for Coders" course at fast.ai It's free :) It gives you an excellent feel for what is possible and they are very focused on solving interesting and practical problems right away. They explicitly try to take the "requires a math PhD" out of deep learning. Once you're through with the course you have a very solid practical overview and understanding and can solve tons of real world problems (it's almost a startup idea generator tbh.) and once you're at that stage it becomes tons easier to dive deep into specific algorithms and optimizations. tl;dr: Take the course (they also walk you through setting up a AWS GPU server so no fancy hardware required) and you'll be able to solve real world problems with state of the art algorithms.