This IS for D2, however I don't think that item generation in D3 will be that much different. Also, this tutorial is a great place to start if you are unfimiliar with the way loot is generated within Diablo games.
As far as item generation in crafting goes, I don't have beta account, but I do believe you get possible damage range when you choose to craft an item. It goes something like this
Awesome Sword of Awesomeness
2 - 4 damage
1.20 attacks per second
+2 random properties
So, that means you already get the minimal and maximal damage that items can have, at this stage. Because all mods are awarded to the item after it is crafted, that means that the it hasn't been rewared any random properties yet. Damage that weapon will do when it hits an enemy is a random number between its minimal and maximal damage, including the minimal and maximal damage, though the game tends to roll middle numbers more often.
That weapons average damage is (mindmg + maxdmg)/2. That is the average damage that weapon will do over a span of time. That weapons DPS (damage per second) is ((mindmg + maxdmg)/2) * attack_speed). So, if the weapon has 2 to 4 damage, and 1.2 attack speed, that means that its average damage it will do will be 3 and its DPS will be ((2 + 4)/2)*1.2) = 3.6 damage per second.
Those are all base stats that weapon has, however, once you craft it, the same way when you kill a monster, item is generated, and it is awarded those two random properties from the large pool of properties. Then those 2 (or any other number it says on that tooltip, it doesn't have to be 2) are put on item as mods, which means that they modify that item. So, if you get +2 fire damage, that means that damage type of that weapon will be changed from physical to fire, and the weapon will gain +2 damage on its minimal and maximal damage. This will all be reflected on the tooltip, though. Same thing if your weapon gets mod which enhances your attack speed, then the weapon will have higher number of attacks in a second, which will translate to higher DPS.
I hope that I have helped you become a better Diablo player. And if you already knew a lot, or all of this, then I apologise, I didn't mean to sound condescending.
Yes I know, I will PM you since the admins here do not like linking to other web sites.
Good things will come to DiabloNut soon. I agree though, at the moment you should supplement its use with other sites for maximum comfort. I talked to Elly about linking to a certain other dataminer site, but I didn't get an answer yet.
As for the topic, D3's item generator is still somewhat of a mystery. However it's already very clear that there's a direct correlation between item level and affix level. An affix with a level of 10 may only spawn on an item with a level of 10 or more. Low level affixes may still spawn on high level items. I'm not sure what determines the level of items a monster may drop, but it wouldn't surprise me if it would only depend on monster level. Whether area level makes a difference or whether it even exists, I don't know.
Here we have the broad axe that can be crafted. If i remember correctly an item can have both an +Intelligence and +Strength affix at the same time but it can't have +fire damage and +cold damage at the same time. Is there any rule that decides what can and can't be combined?
Is there any way (other than experience) to know which affixes can be combined and which can't?
Here are some of the rules I know. They're based on my observations and the third may not be true.
As you've said, a weapon may only have one elemental mod.
A given affix may only spawn once on an item, primary and secondary versions aren't an exception to this rule. This means that you can't have a primary VIT bonus and a secondary VIT bonus on the same item.
I'm not sure about this, but I think that the first two slots of a Magic item (the visible prefix and suffix) will be filled with primary affixes if possible and the other slots (crafted Magics may have more than two affix slots) will always be filled with secondary affixes.
If you want to look at the list of items which may carry a given affix, check out the link Grayson Carlyle posted and click on an affix that you want to know more about.
So if I'm right, then for example a Magic item with two affix slots may only have either STR or DEX, since all attribute bonuses are suffixes. A Magic item with three affix slots could spawn with a primary STR bonus and a secondary DEX bonus.
It's unknown how many primary bonuses Rare items may carry or how exactly are they generated.