I will give you my thoughts and experience, hope it helps. I am sure others have better, different, or more applicable information, but here are my two cents. You may already know this stuff, but here it is just in case it can help you or someone else.
I built grousers and tracks for a Frandee. I realize yours are different (more modern), but if you are going to build your own here are a few things to think about. The Frandee style are wood (I am sure you aren't going with wood, just my case) with a one inch wide steel wear plate on top that contacts the ground/surface. This is great for spinning donuts/cookies and they do fairly well in the snow. However, they side slip badly, especially on hard pack or ice. There are essentially dozens of little one inch wide 32 inch long skis supporting the cat. This has put me in a predicament or two over the years. So based on this, look at the sharper grousers and ones that have a feature to help limit side slippage. As mentioned these are old school design, they stopped making this style probably because of this issue.
Belting: I purchased belting that is 12" wide and was rated for very low temperature from Kaman Industrial Supply. The belting is what is used for grain elevators. It has a very thin (I think 1/16") rubber skin on BOTH sides because the grain is not to abrasive on the belting so they can get away with this. There is also belting that has one or both sides where the rubber is much thicker, this is for handling abrasive materials (rocks, gravel, etc.). I would stay away from this material, it is not needed, robs power, and adds unnecessary weight. My Frandee uses two 12" wide belts per track, I think they are 4 ply. So for both tracks I purchased 100 feet of belting for around $1000 about 5 years ago. Fasteners, my grousers and tire guides are each held on with 10 screws each. In my case strong fasteners are NOT needed, I used light duty grade 2 stuff, and I needed about $1000 worth of screws, washers, and nuts (Mcmaster Carr) for one set of tracks. I also purchased the joining hardware for the belting ends from Kaman (that was a few hundred more dollars). My tracks have held up well, I have over 500 miles on them now and have had no issues with the belting. Be involved in purchasing the belting, do not trust some farm equipment belting supplier, the ones I tried to work with had no idea about temperature ratings or what was all available. Not saying all are like this, I am sure there are very good ones out there, just our local one was no help. Kaman let me look through their literature and we were able to pick out a good material.
I would check the tire guides close for cracks and brakes very closely before reusing them. The majority of my tire guides had to be straightened, repair welded, or made new. Running the wrong tires on the cat can destroy the tire guides. I caution anyone running a Frandee style cat, do not use those old lugged military tires, even though they are the correct size the tires guides do not run on them correctly and the guides get destroyed, ask me how I know. Because my cat had those on it when I got it and the guides were trashed.
Holes in the belting, you do not need to pay some company to drill the holes unless you want to. It is very easy to do. What you do is build a template and drill bit and layout the spacing then drill your own. I used a piece of one inch wide 1/8" thick steel that was the same width as the completed track. I drilled holes in this bar where the bolt holes had to be. Then you layout the spacing on the belting and set the template on the line and drill through using a special bit with a piece of wood on the back side for the drill to go into. The special bit is the secret weapon. figure out what size of hole you need, say 1/4" diameter, find a piece of steel tubing that diameter then sharpen one end so it is a knife edge, NO serrations are necessary. Now put that in your drill and drill away, makes great holes, you will have to clear the plugs out of the tube once in awhile. I do not think I used any lubricant, but one could if they wanted. I also think I had the bevel for the knife edge on the OD of the tube.
Here are some photos of my tracks, when I got them (trash) and when I built them ($10K later):
