D2 modding has some hard coded effects when it comes to mods that spawn on items, but whether you want 1-3 big effects or lots of small effects, many options possible.
- Effects - These are from itemstatcost.txt. For example, +X%EnhancedMaximumDamage and +X%EnhancedDamage are two different Effects. Most item mod descriptions are for each Effect, but some groups of Effects are collapsed into a single description (e.g. PoisDmg and PoisDuration become "+PoisDmg over X seconds"). It's possible to create new Effects (i.e. itemstats), but usually they have to follow some precedent in the game (i.e. the new +MinDmg/Lvl itemstats are just clones of the +MaxDmg/Lvl itemstats with a few minor changes), or they can be arbitrary and only used in soft-coded ways (e.g. "+%MagicDamage" is referenced only by a few skills in Skills.txt by using some algebra to rewrite their Synergy field)
- Properties - These are from Properties.txt. Each Property can have up to 7 Effects (e.g. Property %ResAll is 4 effects - one for each of Fire, Cold, Ltng, and Pois Resistance).
- Affixes - These are either Prefixes, Suffixes, or Automods (these always appear on White, Magic, Rare, and Crafted items). Each Affix can have at most 3 Properties. Each Affix belongs to a Group, and an item can never spawn with more than 1 Affix per Group (e.g. you could make a %ResAll Automod and %ResAll Prefix and prevent both from spawning on an item by using the same Group number for each). It's possible to set Prefixes and Suffixes to not spawn on rare items (only Magic). It's possible to set a minimum and maximum level for an affix to limit when it can spawn (this seems to be ignored only for Automods when re-rolling via the Cube).
Note that these links go to ArreatSummit, and some of that information isn't relevant to all D2 Mods.
- Magic Items - Spawn with up to 2 Affixes (50%Suffix, 25%Prefix, 25%Both). If you wanted a mod where items only ever had 1-3 big Effects, then you could set all Prefixes to have 1 big effect, all Suffixes to have 1-2 big effects, and prevent these affixes from spawning on Rares.
- Rare Items - Spawn with up to 6 Affixes (50%Suffix/Prefix, but never more than 3 of each (i.e. a 4th Suffix would be dropped and result in a Rare with 3-5 Affixes)). In HUv1.7, the limit of 3 Prefixes and 3 Suffixes was used by giving an important Property (e.g. %EDmg) to all Affixes (so Rares would have up to 6 stacks of this mod), another important Property (e.g. +1 AllSkills) to all Prefixes (so Rares would have up to 3 stacks of this mod), while leaving the last available Property to maintain the flavour of that Affix (e.g. +ColdDmgToAttack)
- Crafted Items - Spawn with up to 4 Affixes and up to 5 Properties. D2 is hardcoded to add 10 LevelRequirement to the item, with +3Lvl per Affix. The only reason to have cube recipes that result in "Crafted" items is if you really want the orange text and extra level requirement. Your crafting recipes could output Magic or Rare items with the extra 5 Properties but with regular text and no level requirement.
- Note that if the crafted item spawns with 3 Prefixes (or Suffixes), but you only have 2 groups for that affix (i.e. after taking one from each group the game will look for and fail to find the last one), then D2 will crash.
- Set Items - Spawn with up to 9 Properties (no Automods). You can add up to 2 Properties for each additional SetItem (i.e. up to 15 Properties per item for sets with 4 items), up to the 6th SetItem. The Set's mods that appear off-item can add up to 2 Properties for each extra item (e.g. 10 Properties for a Set with 6 Items). Sets can have up to 8 Properties upon completion. Note that some Effects behave strangely if they aren't on an item (e.g. oSkills don't have a level requirement, +%Defense doesn't have an effect), so you pretty much have to test anything new to see if it'll even work.
- Unique Items - Spawn with up to 12 Properties (no Automods)