A question I get asked frequently is what stones to get. The rabbit hole of sharpening is even deeper than the rabbit hole of Japanese knives, so we won’t get too deep into the weeds. Generally, the idea goes: 1000 grit is good for refinishing/touching up knives that are starting to feel dull. If you have chips or a knife that has been neglected, you probably want to start as low as 220 grit. And for finishing and polishing, most people won’t need higher than a 3000 grit stone for most applications.
I say “generally” because different brands and stones may not have the same definition of grit. The type of abrasive material used as well as the type of material used to hold the abrasive material together will affect the roughness, hardness, and durability of the stone differently. A shapton glass 1000 grit feels vastly different than a King deluxe 1000 grit.
For all intents and purposes, most people will do fine with having a 220 grit, 600 grit, 1000 grit, and leather strop. A good starting point would be a 600 grit or 1000 grit stone. I would avoid the generic blue combo whetstones sold on Amazon though. I haven’t had very good experiences with them.
I’m going to link to a 220 grit Shapton whetstone below. It is quite rough compared to the other stones I’ve recommended so far. But this is necessary for the rough sharpening required on blades that need a lot of work. This stone doesn’t work as fast as a shapton glass stone, but it doesn’t dish as fast, meaning you won’t need to flatten it as often, so it is a little bit of a trade off. The feedback I get from this knife is pretty nice. And the price isn't too bad as it can be had for under $40USD.