What do the guild augment slots do exactly? I've found stuff with it before. How do I get the items to combine with it?
The guild venders in house K sell crystals that can be attached in the stone of change (found by the bank in the marketplace). Each crystal lasts 6 hours, counting any time you are logged into that character, but they are pretty cheap. The types of crystals you can use vary depending on the item. I currently use a weapon slot (elemental damage) and a ring slot (bonus HP).
You need a minimum guild level to even equip items with the slots, even without a crystal. Level 45 is when mediums kick in and they become worthwhile (IMO).
Wiki entry on them.
The guild slots last when you disjunction an item and so you can craft new items with the guild slots attached. This means anything with a small or better slot might be worth extra money on the auction house. The same goes for special item materials (like silver weapons).
How common are Chaotic enemies? If they aren't too common, I might go back to using my awesome entropy-inducing True Chaos weapons of "vaporize in a cloud of lightning and plasma" over my slightly-more-powerful bland equivilants.
It really depends where you are. Certain quests will be full of them, other times you can run an entire adventure pack without a single one. I wouldn't rely on any single weapon or weapon set. Having something that will cover the weaknesses of your main beaters is well worthwhile.
How exactly does one customize a "craftable" weapon? Does that just mean the prefixes and suffixes can be changed?
It depends.
Generally you take any basic weapon, disjunction it to become a craftable blank, removing all current effects, then add a prefix, suffix and enchantment bonus (+X). The added effects have to be crafted as shards, which is where the actual crafting comes into things.
Some items will come with an extra craftable space. These can have an extra prefix and suffix added on top of existing effects.
The main limitation is the crafting potential of each item. Items with space included tend to have a potential of 3 that can't be changed. Disjunctioned items start with a potential of 5. This can be increased up to 15, but that's very expensive. 13 is the highest I've ever gone and that costs 750 Essences.
Each effect you add has an associated potential cost. The sum of your added effects has to be lower than the total crafting potential you have on the blank. This is then related back to the minimum level of the item as ML = (2 x potential) - 1.
An example item;
+3 Holy Silver Weapon of Lawful Outsider Bane
+3 - 3 potential
Holy - 2 potential
LOB - 2 potential
Total potential - 7
Minimum level - 13
This means you need to add +6 and +7 potential shards before adding the other effects. The blank used here would be a silver weapon of whatever type you most enjoy using.
Somebody was showing off a docent earlier that had a required (not absolute) race of human or half-elf--ouch. So only a Warforged with a very high Use Magic Device could forge the check and use it?
Yeah. This is an old bug that was meant to have been fixed in the latest update but doesn't seem to have been. Similar you can get non-docent armours with required-race Warforged.
There are also Dwarven Axes with required-race non-Dwarf, which is just annoying.