Reddit mentions of Japanese Cooking: Contemporary & Traditional [Simple, Delicious, and Vegan]

Love Japanese food. This book taught me loads :)

If you're just using it for miso, you don't need to marinade or even really cook it. You could cut a block into about 8 pieces and freeze it for maximum use (though that will change the texture a lot). Just slice into small cubes and simmer in the dashi or broth before you add the miso paste (stir a spoonful in a bowl with a little dashi, and add it right before you turn off the heat).

You might be able to buy dried shiitake online. Probably more expensive in the UK, but I got a huge jar of sliced and dried mushrooms from Amazon and the whole thing lives in the freezer. I soak about 6 pieces in water for half an hour to make a basic base for miso.

If you're in a large city, look for Asian grocery stores. Most cities will have at least one, and you'll probably find tofu much cheaper.

And yes, that's the konbu you want (that you linked). It lasts for ever, and expands a ton. You probably only need about a square inch per bowl of soup.

Check out this book. It's incredibly simple, all vegan Japanese cooking which doesn't rely too heavily on obscure ingredients. You can figure out some substitutions for lots of the veggies she suggests, but I found it an easy way to understand the typical flavors of a meal without too much effort.

Ninja edit: one of the awesome things about miso paste (I love the white variety) is that it lasts for bloody ages in the fridge (like a year or more if you store it in a zip lock bag). So many of these ingredients that look pricey are actually extremely cheap considering how much use you'll get out of them.

I checked out this book from the library a few years back and really enjoyed the few recipes I made from it. The "calamari" is amazing!

I've heard good things about Kansha as well but have yet to read it.