Is the Miyabi Koh chef's knife good for beginners?

It can be, but it demands good habits. The hard, thin edge rewards proper cutting technique and punishes twisting, bones and frozen food. A softer Western knife is more forgiving for a first good knife.

How does it compare with the Miyabi Birchwood or Black lines?

Those use SG2 powdered steel at higher hardness with more elaborate handles and cost more. The Koh uses a simpler stainless steel at about 61 HRC, so it is a step below in edge retention and finish but easier to sharpen and maintain.

Can I put it in the dishwasher?

No. Hand wash and dry it right away. Dishwasher heat, moisture and detergent dull the edge and can crack or warp the wood handle.

What can I cut with it?

Vegetables, fruit, boneless meat, fish and herbs. Avoid bones, frozen food, nuts and hard squash skins, and use a wood or plastic board rather than glass or stone.

How should I sharpen and maintain it?

Hone lightly and sharpen on water stones or with a guided system suited to hard steel. Avoid pull-through carbide sharpeners, which remove too much metal. Oil the wood handle occasionally.