Hi Sebastian, have you tried to set the height of each section or item to 100vh? It will be the height of 1 screen no matter on which device you are.
Put a small element in the middle (center) of each section, when it enters the viewport you could make the right buttons appear by changing the label and text. (using viewport enter)
If you are familiar repeaters and connecting them to a database, each screen could be one item in a repeater. That would save some work as you only have to a add the elements and code once.
If you also want to make the buttons fade in and out like on the website you mentioned, I would use an array of promises, which gives you more control over when to fade in and out. This would be a bit more complex, and it might be easier to leave the fading effects.