Minecraft wiki entry for Starting_in_the_Nether, associated text: Ghasts drop gunpowder, which is used to make splash potions.
Once you get some coal from wither skeletons, you can use it to build a campfire. When you break it you should get two charcoal every time.
Use fence gates instead of doors. Magma cubes can't jump over them, but you can hit over them. Piglins can open doors but not fence gates, so put a trapdoor above the fence so you can flip it down if piglins or blazes are shooting at you over the gate.
Don't let hard mode burn you out. Try easy mode just to see what it's like, even if you're used to hard mode. It can make a difference, especially earlier in the game. Roll a dice and set it accordingly, if you like.