For the record, for crazy overpowered weapons/armour, whilst Smithing level 100 and Enchanting level 100 is recommended (especially for the double enchantments per item perk that you get maxing Enchanting), imo Alchemy 100 isn't necessary.
I'm only level 46 or so Alchemy but I managed to buy numerous Enchantment Elixers from vendors (+25% Enchantment). Just save game in-front of an alchemist, buy the elixer if they have it, save game again, kill them, load last save and rinse repeat. Each time you kill them, when you re-load the save just before you killed them, for some reason all the vendors money and items refresh. An easy way to get all the items you want from vendors is to keep doing this till the one you want shows up.
Once you have the Enchantment Elixer, get to an Enchantment desk and take the potion (if you're super quick you can do it in a single potion, but two is recommended). You enchant the following (certain items can't have both so just do the one) with
Clothes - Fortify Smithing only (+28%)
Hat/helmet/circlet - Fortify Alchemy only (+28%)
Necklace - Fortify Smithing and Alchemy (+28%)
Braces/Gloves/Gauntlets - Fortify Smithing and Alchemy (+28%)
Ring - Fortify Smithing and Alchemy (+28%)
Wearing the above gives you +112% Smithing and +112% Alchemy.
You don't need the Alchemy enchantments for the build, but I say do them just so you can easily level up Alchemy using the above gear at a later time. It's basically the ultimate outfit for any time you want to do Smithing or Potion making.
Wearing the above, take a Blacksmiths Elixer (an additional +50%) and when upgrading your armour/weapons (doesn't make a difference to initially forging them) and you'll have ridiculously powerful vanilla gear.
Then whilst still wearing your Enchanters outfit, take another Enchantment Elixer before Enchanting your new smithed weapons and armour for the (near) ultimate set up.
Only way to make better equipment is a longer winded set up that also requires level 100 Alchemy for a negligible difference in armour/weapon potency.