The guy has way too many calibers. If just starting out, limit to 4 calibers only, and get several guns for each caliber. Once you have the basics covered in both ammo quantity and guns for each caliber, then start expanding your caliber selection.
For instance, 22lr guns are available in both rifle and pistol. Same for 38/357, 223/5.56, 300AAC, and 7.62X39.
Stay with one shotgun ammo (12 or 20, etc).
If I ever buy a gun or start a “collection”, this is what I would do. Buying 20 different calibers of ammo is silly, and the article doesn’t even mention 7.62X39, the most widely used caliber worldwide.
Concur, I would argue on 2 to 5 calibers in each class, then build up a large supply of ammo for that. It is pretty expensive having dozens of different types of ammo. Keep it simple to start then expand if you see the need.