You want as many saplings planted as possible because at the beginning you will spend most of your time waiting for trees to grow. Make sure to keep your Grass safe because it's all you're going to get.
You can build downward by crawling (using trapdoors) and placing blocks on the bottom of top-half slabs. At a low Y level, mobs spawn faster, and you're going to need a lot of mob spawns. Also, Phantoms won't spawn when you're below sea level.
Have an Enderman Pick up a Grass Block and kill it to obtain the Grass Block as an item. Bring the grass and some dirt down to build to the world bottom and make a grassy spawn platform for passive mobs. When you get Pigs to spawn, start breeding them -- you will need to convert them into Zombified Piglins.
You're going to need 10 Iron to make a Cauldron and a Bucket. Each Zombie killed by a player has a 1/120 chance to drop an Iron Ingot (player kills, not fall damage). That on average means you need to kill 1200 Zombies. It's hard to move Mobs without Water or Pistons, so you'll likely have to rely on pathfinding mechanics to make a farm. This video by ilmango is a good place to start.
Once you have 7 Iron, craft a Cauldron. When nearby a player, a Cauldron has a 1/81920 chance each tick to fill with single layer of water when rained upon. This means a single Cauldron takes over 3 hours of raining time to fully fill with water on average. As you wait for the Cauldron to fill, continue killing Zombies to get enough Iron for a bucket. A single Water source can be duplicated a few ways, such as by using Water Bottles to fill the Cauldron or by placing the Water source on the top of a 2-tall hole and growing Seagrass on the bottom.
You will want a Lightning Rod to help converting Pigs into Zombified Piglins for Gold. Kill Drowneds for the Copper to make one.
Pigs convert into Zombified Piglins when Lighting strikes within 4 blocks of them. You need 16 Gold Ingots or 144 Gold Nuggets to craft 2 Golden Apples. Zombified Piglins drop 0.725 Gold Nuggets on average when killed without looting, so you need to convert about 200 Pigs. Craft 2 Golden Apples once you have enough gold.
Isolate 2 Zombie Villagers to be cured. Then get a Witch in a Boat. If you join a Witch in a Boat, the Witch will still throw her potions, but can't hit you. If you have less than 8 half-hearts of health, a Witch can throw a weakness potion. Use a weakness potion thrown by a Witch and the Golden Apples you crafted to cure the Zombie Villagers.
Ensure you have a safe supply of villagers. Trade for Emeralds so Wandering Traders can be utilized.
Kill a Pillager captain at a Pillager Outpost to get the Bad Omen effect, then start and defeat a raid by entering a " Village". Once you have the Hero of the Village effect, stand by a Toolsmith and they may gift you a Lava Bucket.
Get 10 Lava, either through Hero of the Village Gifts or by buying Pointed Dripstone from the Wandering Trader. Use the Lava to make a Nether Portal frame. Light the portal with Lightning or using Lava to set wood on fire adjacent to the frame.
Obtain Blaze Powder by killing Blazes that spawn in Nether Fortresses. You can then craft Eyes of Ender, complete an End Portal, and kill the Ender Dragon.