This program "only" consists of 2 movements, the kettlebell swing and the turkish get-up. But it's deceptively challenging. Progressive overload with S&S is mainly in building up the swings and in perfecting the form of the TGU. Once you have mastery with a kettlebell of a certain size, you test yourself and move up to the next size. It used to have time requirements, in version 1, but that has been removed in the latest iteration.
Kettlebells, traditionally, jump in 4kg increments. So, on average, with this program, you start with a single 16kg kettlebell, and then move to a 20kg, on up to 32kg.
I have a lot of kettlebells... 2x12kg, 2x16kg, 2x20kg, 1x24kg, 1x28kg, 1x32kg, 1x36kg, 1x40kg. They have a small footprint. I leave them all in a corner in the garage and they take up very little space, maybe 3 square feet. I'm on a different (non-kettlebell) program right now. But, I am using the 32kg on days that are not my main training days for strength-endurance purposes (I like doing between 300 and 500 heavy swings a week).
Sorry for the brevity, but I wanted to respond. Hope it helps.