Regarding the landing and take off distances 1 yard for small fences 80,90 a yard and a half for bigger ones 120 and starting 130 you can count 2 yards for takeoff and landing. 4 yards for each stride in between fences that is 12 foot. If at the end of counting you find extra or missing yards hence its a trick by the course designer and you will have to adjust your horse's stride to fit that.

Take a step out from the middle of the jump don't count that step as it is where the horse lands and then start counting steps so every four steps u take is a horse stride and then when u are at the end take one step away from the second part of the combination as this will be the take off point so don't count that step either