Gouache actually works on black paper, since it can be used thicker than the typical application of watercolour 😊 I'm not sure the weight or tooth of the paper in the Sakura sketchbook, but it should still work pretty decently with gouache as long as you use a higher paint:water ratio. I think you'll have a lot of fun playing around on the black paper! In the future I would recommend searching for watercolour sketchbooks specifically (not sure if the Sakura one you got is a watercolour one). The paper is thicker and made to handle water so you can play around more with your gouache; using it thinner like watercolour and thicker with less water without worrying about the paper warping too much. I recommend 100% cotton paper, just because watercolour does behave differently on cotton vs cellulose paper, but cellulose is cheaper and still works perfectly fine! Especially when you're still learning. You just wanna look for the "watercolour" part when looking for your next sketchbook. Hot press watercolour paper is going to be smoother (the brand Paul Rubens usually sells some affordable options) and cold pressed watercolour paper is going to have more texture. Both handle the paints differently, but you might personally prefer one over the other. Sketchbooks with watercolour paper can handle all kinds of mediums, even acrylic and markers, but keep in mind the amount of texture on the paper can affect the nibs on markers over time if there's a lot of it or if it's extra rough! I'm excited to see some of your painting videos in the future! I think you're going to enjoy the gouache a lot 😁 And just in case you haven't heard; the Himi gouche can mold over time. It's recommended by people that use them to open the container pretty often (prob once every 1-2weeks) and give them a spritz with water that has clove oil or an anti-molding agent mixed in. Just a tiny bit! I would even give them a little stir with one of the scoops you got once every couple of weeks to help keep the consistency of the paint once you spritz it 😊