When setting up a course trot poles for my horse are about 4-5 feet(((I literally measured my foot so I could set up poles and I have to take 5 steps heel to toe heel to toe each one and then add the length of my toes)))apart because he has a big step. Other horses may only be 2-3 feet depending on how big their step is.
For cancer poles normally for horses it's pretty much the same for all of them but there are a few outsiders. But what you do it you stand with your heel against the pole and then you take 4 NORMAL walking steps, your next pole or jump should touch the toe of your 4th step.
Listed to your horses feet when they touch the ground. A canter should have 3 sounds of feet hitting the floor in one stride. The back leg, the other back leg at the same time as the front leg diagonally from that leg and the other front leg. When your horse lands with all 4 feet you start counting.until he jumps for the next one. I don't think you need to count strides for trot in a course. Counting the strides is to make sure your horse doesn't jump from to far or to close but with trot the horse can control the length of their strides easier which makes it less likely they will jump from a weird distance.