I highly recommend you take a show handling class or three. Hopefully you have some dog clubs in your area that put these on.
There is something called the "hard stack", it is most often seen in the toy group of dogs. THe handlers kneel down beside their dog and place the dog in the correct stack position.
When teaching stack you start from there - ie the hard stack position. Using the blocks is a wonderfull tool to build up their stance strength. But make sure you are training the stack position correctly. TAlk to your mentor, and show how you are stacking your boy.
For the ultimate "free stack" it occurs over many many many times of practice. I use Stand - Stay. I use these two commands as they are also used in obedience training. You can trot with your pup, then slow down and say Stand - Stay. You want the dog to stand still. First you reward for standing Still ie the stay command. Then you work on feet placement, if you are lucky all your block work will translate to a natural stack pattern for your puppy. Then you can slowly if the feet position is not correct walk 1/4 or 1/2 step forward and guide your dog into the correct stance.
You really need to videotape yourself and him in practice runs. Have your wife help you - ie she could be the videographer. What you want to practice is the correct speed for your dog with you on the trot. Correct speed means that which shows off your boys side gait and front n back to his best. Try out different speeds, see his gait at slow, moderate, fast. Now for Yorkies especially you will be looking at your own gait stride, relative to your Yorkies; stride. I think their is a video of me somewhere on here showing my yorkie, also some pics. Look at the length of my stride. My boy is a very very fine mover, and even though he is 9 inches tall and I am 5 3 I go to the limit of my stride length to show him off. You are likely taller than myself (hey who isn't)
so might not need to do full strides.
The down n back is very Key. It is often where dogs fall apart. By that I mean when structural anomalies are most apparent. You don't want to see cross stepping, sidewinding, rough movement or a jarring type movement. The dogs head should naturally be held high - especially for a Yorkie.
Look at your dogs natural movement. off lead in your backyard for instance, and videotape it.
A show dog needs to be an athlete - again in my opinion. They need to have great exercise overall, and specific exercise to enhance their gaiting. THey need to be incredibly well socialized and get used to strange places, people smells and noises.
Some dog shows put on fun matches, try to find some in your area.
Now I am going to say something that might be hard to hear. It does not look like you are wrapping this boys coat. His facial furnishings are quite short. ANd that shortness will be a negative, even though he is still a puppy, and I don';t know when you plan to start showing him. But you have what you have, you need to know you will need something else to offset that shortness. THat something must be a lovely gleaming coat, correctly groomed, coupled with a great structure which should be evidenced by his movement. You can look at my video here, Razzle my Road to a Grand Champion. Look at his coat. And like your dog he has short moustaches, but he had and has other qualities.
In the picture you posted your boys coat was dull, looked like he had fly away hair, and the hair was wavey. That needs to be addressed if that is how he normally looks. Show dogs need to be washed if not weekly every other week. They need top quality food to feed that coat, and correct exercise.
It is not easy to be a show breeder, I do hope you have gone to shows and seen the grooming and Yorkies in the ring.
In my avatar you will see pics of Razz when he was a puppy, look at his coat it gleams in the light, and I dock dived with him, rallied, and obedience trained him, while he was being shown.
I know it seems daunting, and it is. BUt you can do this, if your heart and mind are truly want this.