Glad to hear the progress! I know the fake treat trick works all the time.
They won't give up an opportunity for a treat, so even if there is a chance there is nothing, they will still go for it. I do it all the time still with Uni.
The sit, I think you are holding the treat up too high. Hold it in front of his nose, then slowly bring it up just over his head, so when he tries to look at it, he rocks backwards onto his butt.
The leash thing, I have no tips, Uni is a crazy girl with walking.