One disc was fine for me, the one that came with the grinder. There are loads or technique videos but I don't see why, it's not that hard! Maybe practice on a spare rim first if you have one. For deeper grinds you want a bigger angle, say 45+, and for shallower grinds, a smaller angle. Don't try and grind it all in one go and don't go over the same spot repeatedly. Have fun, and be careful. Goggles might be a good idea if you can get any.