This post took me back. I haven't posted in years but I used make very similar threads before I started studying design. If you are serious about designing shoes I would recommend that you start researching Industrial Design first, and specialize on footwear design later. Unless you live in Oregon or NY, it may be hard to find a specific footwear design program or school. You can focus on shoes while studying Industrial Design but I would encourage you to stay versatile. Shoes are my specialty and favorite thing to draw, but I still practice drawing all sorts of products(coffeemakers, clothing irons, cars, furniture etc..). Keep sketching, all day, every day, but make sure you are learning and practicing good techniques(look into digital sketching). Core77, Spencer Nugent's sketch-a-day videos, and TheSketchMonkey videos on youtube will take you to another level. Also, doing research on how shoes are made will help you in creating more realistic designs.
I graduated with a Bachelors in Industrial Design 4 years ago and it was the best thing I ever did for myself. School is crazy expensive(still paying student loans) and job market is unbelievably competitive, but the work is awesome and I make a great living at 28. The decision you will have to make is whether you want to study Industrial Design or Fashion Design. Fashion Design is great, but I think Industrial Design will give you a more diverse set of skills. Happy to help if I can and keep up the creative sketches. Good luck!