I use a 9k stone and sharpen for like 10 seconds, so its not that much material. I have an extremely high standard of sharpness.
For the first 30 mins to an hour of work, the edge absolutely flies through food. (Hair whittling/hair popping)
Afterwards its still very sharp and cuts very well ( clean shaving)
Then it starts to struggle with tough skins and delicate foods (bell peppers, tomatoes, etc) this is usually where it stops shaving.
I like to keep my knives so sharp that it flies through everything.
Coarse diamond stone and a thin cheap knife. The coarse stone is fast so you get immediate results and feedback, which is crucial for learning. You want to use a cheap knife since you can damage knives with bad technique. Cheap knives are also softer and sharpen faster
Diamond plates are much more straightforward than waterstones. You dont need to soak it, water it, flatten it, etc. They aren't necessarily better, but they require much less maintenance
Also I highly recommend freehand. Youll always encounter a knive that doesn't work with this, or that system, but you can sharpen every knife, tool, scissors, etc, on a normal sharpening stone.