Foot position is mostly relative, but usually the most comfortable one is with your shooting side is turned to the basket ever so slightly.
Form shooting close to the basket, somewhere maybe around the edge of the circle, starting with the knees bent is one thing that's helped me keep the lower body mechanics consistent over the years. Then, you try to shoot free throws the same way. It's all about muscle memory really, and mental awareness while you drill yourself. Put your whole mind into each shot. Start from a small number then slowly build up. If you try to shoot too much too soon, your mind will focus on the number you're aiming for and not the mechanics that you want to ingrain.
Btw, I just find it awesome that you're this determined to learn/play ball even if it's somewhat late. Keep it up, man.