Rather than starting with a number of things you want to have in each category, try paring it down until you can't have any fewer. For example, you could have armor in the Light, Medium, and Heavy categories. If you want Mail to behave differently from Scale somehow, start by calling it Medium armor and then add some modifier because it's Scale. That way a gaming group could get away with saying "we're gonna do a simple game this time, no armor type modifications." With weapons, you could probably pare it down to 15 types and still capture a lot of variety. Is a quarterstaff so very different from a bo staff? Perhaps you could list weapons based on what they do, so you have "Cleaving" weapons, and then a pick does +1 vs. stone and an axe does +1 vs. wood.
Taken to the logical conclusion, you could get away with "generic melee weapon", "generic ranged weapon", and "armor". No names, no types, just numbers. I actually tried this for a while and...well...people hated it. Players love variety, and I've provided it by making each weapon/armor/etc. different in how they interact. The falchion is a one-handed sword that ignores nonmetal armor, because it's a cross between a sword and a hatchet. The greatsword is two handed, deals much more damage, but causes you to take a Velocity (Initiative, for D&D players,) penalty. The estoc is a sword meant specifically to ignore plate armor, but it's not as useful against chain or banded mail, or what have you. There are a ton of spears, but they all do different things. Example: You can use the low powered Guisarme to trip your opponent and leave them defenseless for a round, or use a halberd to devastating effect against mounted enemies. There are a couple dozen accessories in the "armor" category, like rings, bracelets, pauldrons and sabatons, but they're mostly stackable enchantment fodder. Finally, I stuck with wanting 100 weapon and armor types for a really simple reason. It makes random item lists really easy.
As for material types, I really do suggest giving each material a modifier to apply to the weapon. Perhaps one material is hard to damage but brittle, so that when you damage it it usually breaks. Each one can have a modifier for weapons and one for armor. Again, the group can easily create new materials and apply the template to all the existing equipment. Or add new equipment and apply the old templates to it.
This is already going in. Spot on.
You could have a second set of templates for condition. "New", "Shoddy", "Rusty", "Broken", etc. This lets someone buy a really nice leather handbag for more money and it has a mechanical effect in the game. Or they can ignore the condition templates to make the game simpler.
This is already sort of in, but equipment wear isn't. If someone fails a crafting check by a small margin, they can produce "flawed", "shoddy" or "crude" items. They take a penalty to the power of the item (damage for weapons, defense for armor,) but it beats losing the materials to scrap. Flawed items can usually be found in shops, shoddy and crude generally are not. That said, if someone overshoots a crafting check, they can produce higher quality gear, up to a certain point.
As for spells - do you have two spells that do the same sort of thing? Cut one. Your canon list of spells is the starting point for people making their own, trying to balance against what's in the system already. You want to describe as many different examples as possible. If you have a both Fireball and a Big Fireball, you're missing out on an opportunity for Buoyancy or Stone Eater.
Magic is kind of a finicky thing in my game. You see, everyone starts with an Elemental Weakness and Affinity. So, if your Affinity is Fire, your weakness would be water. This is kind of a double edged sword in some cases. You can do huge damage with Fire magic, but there are only two healing spells in the whole set, one of which is the Master Spell. (Spells are broken into tiers, Basic, Intermediate, Advanced, and Master.) You could still use Water magic to get the healing spells within, but you're only going to heal half of what you normally would because of your Elemental Weakness. Instead, that player could focus on Life Magic, which does a whole lot of other things (trade Mist Form for Angel Wings, for one,) or go to the (generally) more powerful Ritual Magic, which has a subset of Miracles, but they require reagents to work. There's a lot of choices, with little overlap.
Do you have two monsters that use the same schtick? Cut one. If you have a Giant who can do knockback with his club, or snatch-and-hurl, or throwing boulders, that's very cool mechanically and it should be a different monster from the Orc. If you have both an Orc and a Big Orc you're missing the opportunity to put in a Moon Girl or a Root Dog.
Monsters are pretty well varied. There's a little bit of overlap, but each monster has different drops, to use an MMO term. Whitecaps are weaker than Redcaps (which are vampiric), but can be turned into valuable materials for healing items, which the poisonous Redcap cannot. I'll probably have to go back over my Enemy Combatants (people to fight) list and eliminate a little bit of overlap, but that's going to be a little harder. There are, after all, only so many jobs a person can do.
People who pick up your game and look it over are going to say, "Does this game do something mechanically that's awesome and makes me want to play using these rules?" and "Does this game contain a huge amount of awesome fat stuff that inspires and excites?"
Yes, they are, and I'm doing my best to ensure that the answer to both of those questions is, "Yes."