Now you're getting it, all except this part....The hole spacing is what is different, not the hole size. The hole spacing for the fabric (in this case leather) has to be bigger than the hole spacing on the foam (these holes are where the buttons are going to be) and the deck pad to account for the depth of the holes as well as the folds in the fabric. In other words, if the hole spacing for the foam is 6" tall and 5" wide, the spacing on the fabric needs to be say 9" tall and 8" wide depending on the thickness of the foam you use. The fabric has to not only span the 6" and 5" distances horizontally, it has to also go down a certain distance into the foam. This extra fabric needs to be folded under accordingly and is what makes the tufts. Also, the holes in the foam need to be about 3/4" to accept the buttons and the surrounding leather more readily.
I don't know what to tell you about the suppliers of foam, leather, and buttons. Most upholsterers make their own buttons, which should be size 22, by the way, which is a little bigger than 1/2" in diameter. I would suggest finding a local upholstery shop to make the buttons and get all the other supplies you'll need. Leather can be bought on line at a lot of different places. Just search for leather and don't be surprised at how much this will cost. If you can do what you want to do for under $1000 I will be very surprised. To cut down some of the cost, have the buttons made from a matching vinyl. Making leather covered buttons is very difficult because of the thickness of the leather, and you'll be charged accordingly if you can even find someone to make that many leather covered buttons for you. I know I wouldn't do it for any price.
Just tighten the buttons down slightly to hold them in place at first, and then start to tighten them down completely in stages, a little tighter at a time. As you do this, you will be able to tell exactly how tight to pull them by the way the tufting looks. It also would be easier to use prong style buttons than eye style buttons. I'll post some pictures of the difference tomorrow and tell you why the prongs are easier.
No one lives forever, the trick is creating something that will.