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It depends on what you intend to do with them. For lapping, something coarse would be a better choice. For slurry making, you can buy a finer one.
I find the atoma 400 to be good at both lapping...

They are pretty much the same as DMT. But since you are looking at an order on fine tools, you can also get the atoma plates. They are worth their money.

You can start with the classic norton 4/8k if you live in the American continent. For anywhere else, the naniwa ordered from Japan would be a cheaper but also reliable choice (US post is expensive...