So I've been in a new world (when I haven't been staying with friends who have 4 kids under the age of 7 for the last three weeks), and have been building up a new Challenge. I've been experimenting with a few things, and after tinkering around with Villager mechanics, I think I'll be actually addressing that soon. Up 'til now it's been an area I haven't addressd, but needed to. People have pretty much been following their own rules for it, I would assume.
The basic position would be that you can feel free to avail yourselves of their services, but try to stay within the spirit of the challenge. Because, yes, you COULD get Iron tools rather easily by exploiting available resources, even in a Dirt Hovel stage. In the beginning I was leery of doing this, but after tinkering with Villagers for a while (and ruthlessly culling the herd with a block of sand an a Cacti block to get rid of the damn Clerics) I (finally got a damn Farmer--even two! Only took wiping out all Villagers but four Librarians and the pair of Golems), I've come to the decision that there's not really a good reason not to specifically allow Villager usage, with a few restrictions.
Reasoning is that in Vanilla there aren't any uses for Emeralds outside of Villagers and decorative blocks. On top of that, most mods I've seen only use Emeralds when they're dealing with Villager mechanics.
TL
R (Applies to Vanilla, has not taken mod-added Villagers into consideration)
Feel free to use Villagers, try not to buy items/weapons from Villagers that are outside the tools you can currently craft. This is specifically referring to Vanilla Tool/Weaponsmiths and Armorers, which allow you to get Iron Arms/Armor/Tools, and Diamond Arms/Armor in, potentially, the Dirt Hovel Stage if you have the correct lucky mix of resources and Villagers.
Exceptions: Shears, Compasses, Clocks, getting Villagers to *cook* your meat for you and paying in Emeralds, and *all* Cleric trades (except Redstone) are permitted at any time.
Compasses are useful and you can use them for maps, which are pretty useful sometimes.
At heart, I'm a resource collector. Not an engineer, not a builder, but I love getting *all the things*
So I've spent way too long planting and chopping down Jungle Trees and building up from 4 Saplings that I took a special trip to find to ~30 or so atm. I've gathereed a bunch of cows and dropped them in a hole, I haven't bothered to collect Sheep yet because there are so many of the things all over the place. I had a bunch of eggs but I used them up for feathers so I could trade written books to the Villagers. All 5 of the Vanilla trees are present and in good supply.
The Villagers should now be self-propagating now that they have Farmers to harvest/share food.
.......I'm just waitting impatiently for Shepherds/Fishermen.
I actually have discovered 2 Villages. One started with ~5-7 Villagers, the other has exactly 2. Village 2, on the other hand, started near Hroses. the first Village spawned a Leatherworker not long back, and I've traded up the chain and gotten 4 saddles (I also have a nametag in one of my badly disorganized chests somewhere). I went up to Village 2 and tamed a pair of horses, then went exploring ,hoping to find Donkeys. To my joy, I found a pair. I tamed them, brought them both back to the first Village, where they were issued Chests and shut in a hastily-erected Stable. I plan on getting at least 2 Horses for each stop on my road. That means faster than running travel. woo.
.....makes me wish I could breed horses atm, but noooo.....it has to be golden apple/carrot.
Now my next job is to finish up the roads (yay for Rough Dirt/Gravel for easy, plentiful road-building materials) connecting my starting point, the Village (which has access to both a waterway AND a Ravine, making the cave entrance I was going to make the official Settlement Mine look wimpy by comparison), and Village 2. I WAS going to name my starting Village Altaria, but I'm rapidly coming to the conclusion that that is now the name of the Village, and my starting point is my Personal Estate-to-be.
......I ay have gone slightly overboard planting Sugar Cane, though. 500+ base plants is probably a bit much.
But hey, for the longest time before the Cull, the only decent trades I could make were with the Librarians.
.....if I ever have to build a road through a Desert, I'm probably gonna go with Dirt in the middle, with a pair of Rough Dirt blocks on either side of it, for a nice green strip down the middle.
btw if anyone knows of a way to make Custom NPCs ride/lead Donkeys/Mules I would love to hear it. I would love to have a convoy of merchants making their way between towns. A half dozen or so with packed chests and guards.