Dont buy these stones they are overpriced. they should be around $1-$5, these are cheap 99 cent store junk.

They use the same abrasive as in sand paper. For 5-10 cents a piece of sand paper you can glue it on a piece of wood.

I prefer Japanese water stones, for $18-$25 only get brand names, a good budget brand is King by Matsunaga,

In general 400/1000 is a good combination, as well as 600/1500

If needed I use a coarse Aluminum oxide stone, or a “Puck” not sure what is the grit, but it is pretty soft and cheap $5

But mostly I just use the 1000 King water stone for around $15-$20

Not sure what country you are shipping to but here are some decent stones:

250/1000 King

300 King

Single grit King stones