The enchantments are all random, whether the items are loot on defeated enemies, in chests, or in shop inventories. You just have to keep searching.
The Necklace of the Peerless Squire is an enchanted necklace and can be made by enchanting a necklace (any sort) with Fortify Light Armor enchant. However, for the Peerless Squire, you'll need to max your enchanting level. Peerless Squire will increase Light Armor skill by 25.
Random Items, Daedric artifacts, Daedric sword with full blacksmith+ armor with blacksmith on it, then enchanted with armor with + enchanting
making the best weapons: get alchemy, enchanting and smithy levels to 100. after leveling these follows these steps: 1-make fortify enchanting potions 2-drink up and enchant fortify alchemy items -repeat alot 3- when you get bored of repeating these steps enchant armor with fortify smithy and brew fortify smithy potions 4-drink up and make a boss weapon with your +400 or so points of smithy out of a deadric dagger. (forging the dagger doesn't make it boss, the sharpening of it does by improving the damage to crazy levels)
You have to know it as a spell first, find someone to teach you it, then it will be available as an option while enchanting.
The headsman armor has no codes, anything.
Invisibility Potions and Fortify Health Potions
Boots of any kind can not be enchanted with fortify archery. Fortify archery is limited to helmets, gloves, necklaces, and rings.
No - Light armor is leather, cloth, etc. Plate armor is considered heavy armor.
There is no Dragon Priest Armor, only their masks.
Armor points refer to how effective the armor is against preventing damage, the higher the number, the better.
you have to make it yourself
There is a mod for skyrim which allows you to give your horse armour (it makes your horse practically invincible btw), but without the mod installed, horses can't wear armour.