Indeed the legs are (atleast for me) one of the most vital basics you just GOTTA get right, or else the pony will look..weird..
I'd love to help but I don't even know if my body anatomy is correct.. It feels correct to me lol
Your sketches don't look too far off from my understanding! They really are close to the gen 4 artstyle, so you're on the right path :>
I usually sketch the body in a bean shape! Helps to keep sight on my proportions, so nothing's too long or short