As a Breton, the easiest (no enchantments) way for you to get to the Magic Resist cap of 85% is to: be Breton 25%, Agent of Mara 15%, Lord Stone 25%, Alteration Magic Resist 2/3 (50 Alteration) 20%. That is probably the best reason to go into Alteration, for the MR perks, and then eventually Paralysis.
Armor:
Alteration eventually gives you Dragonhide which hits the cap of 80% physical damage reduction. It takes a while to get there though, and renders the 3/3 Mage Armor perks useless eventually too. Dragonhide takes a while to cast, doesn't last super long (you can get Stability and you can dual cast it also). Before Dragonhide, if you take the Mage Armor perks, your Ebonyflesh will give you 300 armor rating.
Here's something some people don't know. The armor cap is 567 worn armor rating only when you are actually WEARING ARMOR. If you are wearing clothes, the armor cap is actually 667. Each piece of armor gives you a hidden armor bonus of 20, 20, 20, (helmet, boots, gauntlets) and 40 (chest), bringing the effective armor cap to 567 when you wear armor.
This means that 300 Ebonyflesh armor rating is actually 300/667, instead of 300/567. Ebonyflesh only gives you an armor protection of 45%, which is terrible compared to 80%. With the Lord Stone active, you will have 350/667, for 52% reduction.
The answer is, both Alteration and Smithing can give you 80% damage reduction. The Alteration line is more clunky in my opinion, do you skip Mage Armor perks and only have 100 armor all game until you get Dragonhide? Or do you take 3/3 Mage Armor for the mid-game, only to have wasted the perks when you only use Dragonhide later?
You can also combine physical armor rating with Dragonhide (not any Flesh Spells). 80% armor rating, combined with the Dragonhide spell will stack similar to magic/elemental resistances, giving you a physical damage reduction of 96%, which can even further be increased by Block, as well.
Weapons
Mystic Bound Sword is equivalent in damage to an unsmithed Daedric Sword, 14 base damage. If you get your Smithing up to 91, you can create a Daedric Sword, and Smith it to "legendary 1" status, making it's effective base damage 24 instead of 14. This is before any One Handed perks, skill level, or Enchanting effects are applied. Every skill point in One-Handed gives you .5% more damage, so when your One Handed skill is 100, you do 50% more damage. The Bound Sword goes to 21, and the Legendary Sword goes to 36. With 5/5 Armsman, you get 100% more damage, the Bound Sword goes to 42, the Legendary Sword goes to 72. With 160% Fortify One Handed gear, the Bound Sword goes to 109 damage, the Legendary Sword goes to 187. This is excluding any Fortify Smithing potions, or Fortify Smithing enchanted gear. You could purchase a 50% Smithing potion, and find or buy or create 4x25% Smithing gear, to make your Legendary Daedric Sword do an extra base 26 damage, so it starts at 40, instead of 14 or 24 like earlier. That would be "legendary 10" and you would need an effective Smithing skill of 244 to reach. That means in the end-game, you compare a base damage 14 weapon (total damage 109) to a base damage 40 weapon, then add all the Fortify One Handed, Armsman, and 100 One Handed skill damage, giving it a total damage of 416.
If you decide not to take Smithing perks, but still level Smithing up, an Iron Sword when Smithed to Flawless (100 Smithing, no perk) will be equal to the damage of the Bound Sword. An Orcish Sword Smithed to Exquisite (65 Smithing, no perk) will be equal to the damage of the Bound Sword. Skyforge Steel and Elven Swords when Smithed to Superior (31 Smithing, no perk) will be equal to the damage of the Bound Sword. With just the Steel Smithing perk, a Skyforge Steel sword is equal to the Bound Sword at a Smithing level of 22, and surpasses it at 40.
The Bound Sword is great for the early game, it outdamages most other weapons. As you increase your Smithing skill, it becomes weaker in comparison. However, you can easily use the Bound Sword throughout the game, as it still does great damage. It's just that Smithed weapons can become astronomical.
Wow. Why did I write all that!?
TL;DR
You can use Heavy Armor and Smithing or Alteration to get to the Armor Cap, 80% damage reduction. Alteration's will come at the very end of the tree, later game.
You can use Bound Sword or Smithed weapons, Bound does more damage at first, Smithed can probably quadruple the Bound damage by the end-game, but Bound still does enough to play the game with.