Kimchi / Mo-Chu Ka-roo?

You'd be better off trying to find the real thing.

Kochukaru is slightly sweeter and smokier than standard 'ground chilli' and simply substituting it will give you variable results to what your kimchi should traditionally taste like.

If you know what you're doing, and by that I mean you are able to know what Kimchi is meant to taste like and are able to tweak the amount of standard chilli powder you're using perhaps in addition to some sweet and/or smoked paprika you'd probably be able to replicate the flavour and taste of kochukaru in your kimchi.

If you're not at that level of ability (and I mean that with the greatest respect) then you're probably far better off trying to find kochukaru, perhaps at an alternative asian grocers or even online somewhere.

The pepper used in Kim chi is actually pretty variable. Not being able to find the genuine Korean powder locally, I've had good luck with 1.5 tablespoons Paprika, 0.5 teaspoon smoked Paprika, 0.5 teaspoon Arbol chili (a medium cayenne also works) per two quarts napa/bok choy etc. mix.

The Maesri brand will certainly work, as will many others.

There are hundreds of kimchi recipes, and no version is any more authentic than another. Many contain whole or sliced fresh chiles (green and/or red) and may contain other ingredients, without any chile powder at all (sometimes called white kimchi).

The first time I made red kimchi, the only thing I could find in the Asian market was a bag of 2-inch reds marked "dried red chiles" from China. I ground them up and they worked beautifully. If you're looking for smokey notes, chipotle powder or smoked paprika should serve well.