It's not frowned on by me, but I merged layers as I went and like I said previously, I didn't document my steps. The look of the map depends on a few factors: 1) the number of textures/color layers, 2) their placement, layer-wise, and 3) the blending mode for each layer. There are tons of free parchment-y, stone, and wood textures available for free online and really, the best way to get good at this is to just experiment. Like you said, you'll have to learn eventually.