You can use the powder or the liquid. I do it in the sink using hot water - have not had a problem. Once you dye it, block it with towels and lay it out to dry - may take a few days depending on the weather and humidity. The tighter the weave of the wool, the longer you need to leave it in the dye. You can take ragg wool knit and dye it in just a few minutes. I dyed my KOM blowdown and it just barely took enough dye to tone down the lightest color in the camo pattern to just a shade more brown which works well here in Alabama where we never hunt in any snow. If you are going to do something big and expensive, I recommend you test it on a corner before doing the whole garment.
I've never tried to do any patterns. I wonder if using the tye-dye method would work with two colors.