Mock villages in an iron farm only need to be separated by 66 blocks.
There is room to stack 3 villages above sea level. I made a double stack in my iron + gold farm.
This farm was created back in version 1.8 and is still working great in 1.12.1, although now it's an iron+gunpowder farm.
There is even room for another level if you build it deep underground, so you could stack up to 4 villages in one tower.
To get villagers to the upper pods I used nether portals, which also helped me go back and forth to my base for supplies.
Once I had 2 starter villagers in a pod I broke the portal and sealed them in.
I made my pods carrot farms and had a farmer class villager as one of the 2 starters, so they would self-breed unattended and I didn't have to interact with them. This saved me a lot of trouble since I only had to move 24 villagers instead of 60 (2 villagers per pod instead of 10 per village). Also, villagers will self-breed replacements if one dies, which seems to happen for some unknown reason since I now have nitwits in some pods and the farm was built long before nitwits even existed in Minecraft.
As for gathering XP quickly, I use my guardian farm for XP, or go to The End, stand under a 2 tall roof and stare at endermen to gather them in front of me in large groups. With sweeping edge III on a good sword you can make quick work of large groups and get lots of XP and ender pearls.
For killing the wither I usually put a couple of iron golems in the room to soften it up then finish it off with a Smite V sword. Drop 5 or 6 golems in the room and they will do the dirty work for you. Maybe when you get your iron farm working better you could give that a try.
sorry to revive this old post but......corageus i wanted to ask you this question
i made my iron farm 2 of them stacked 66 blocks between them like you said:)
the problem is this that if i go higher in altitute the water will start freezing
how do you deal with this because you can't place blocks on the edge , mobs will start spawning
any ideas ? thank you
The Meaning of Life, the Universe, and Everything.
i have an iron golem farm but its super slow .... i am thinking to building a nother one but i need to make it 100 blocks on top on the each other and the thought of getting the villagers at that hight makes me throw up :D. since i live underground i have a beacon to have haste 2 and eff5 picks to clear out blocks ;). but i want to make 2 beacons and i need a tone of iron but my iron farm is super slow ....
villagers are not a problem since i have my trading center and my villager breeding place
the only one thing i might need is a better exp farm..... i have one from a zombie spawner that i found but you need to afk to much to get the exp so i am thinking of making a new exp farm but efficent one ..... do you have any ideas that you can share ?
but anyway i am glad that helped
P.S this is a tutorial i used to kill the wither but be careful it is not working all the time , last time i almost got killed , it left me with 2 hearts