As to the material packs for KT, they are very good. Good materials to use directly in SU, not so easy to find. If the materials in the material packs for KT work for you, don't worry about what you paint the surfaces with in SU. Replace them once you get to KT.
You can Google for wood grain images and import them into SU to use as materials but often the images are too small or poorly lit so they tile badly. There are a couple of wood grain libraries that have been made for SketchUp but in my opinion, they aren't much better than the materials that come with SketchUp.
FWIW, at least the cherry material that comes with SketchUp is way too large. I don't know why that is but it is easy to edit if you apply it in a model. You can then save the edited material back to the Wood library letting it overwrite the original. The other woodgrain images may suffer the same problem but I don't remember for sure and I believe I delted them anyway.