if I have 100 points in light armor and I'm wearing a ring which gives me +12 to light armor, would it result in my Light Armor skill being 112
Yes. Your modified Light Armor skill is 112.
- For armor skills, each point above 100 is another 0.4% increase to armor. (Mind the 567 armor rating cap).
- For weapon skills, each point above 100 is a percent increase to damage.
- For crafting, each point above 100 increases the outcome when skill is involved. (upgrading, enchanting, etc).
For the other skills, going above 100 may not produce the expected effect. Pickpocketing, in particular, may overflow and give lower chance of success than you'd have with 100 skill.
Ran some console commands in the name of Science!
First, I leveled light armor to see the effect that skill has on armor rating.
Imperial Armor chest
- 25 armor at 15 skill.
- 33 armor at 100 skill.
Well, that's underwhelming. The rest of the numbers in this post are with 100 light armor skill.
Then I maxed smithing and started crafting.
- 74 - 4 piece leather - no perks
- 119 - upgraded with 100 smithing
- 238 - agile defender 5/5 (cleanly doubled the value)
- 357 - custom fit, matching set (and another 50% on top)
So much for unperk-able leather. How about elven?
- 297 - 5 piece elven armor, agile defender 5/5, custom fit, matching set
- 528 - upgraded with 100 smithing, elven smithing perk
- 610 - upgraded with 130 smithing by using Ring of Smithing (+15) and Necklace of Smithing (+15), elven smithing perk
- 537 - same, but shield-less
Elven armor is the lightest armor I'm aware of. 4 piece is 7 units of weight. 5 piece is 11 units of weight. With this low weight, you can easily skip armor weight reducing perks.
Then I headed off to the enchanting station for one last test. I enchanted with fortify armorer and saw no change to armor rating after the enchant. I recommend skipping the arcane blacksmith perk if you are planning to wear only your own crafted armor. Just upgrade before enchanting. (Ignore what the enchanting table tells you about armor rating, it's wrong.)
That's 2 smithing perks, and 7 light armor perks. With 100 skill in light armor and smithing, you'll be level 26 and easily able to afford these perks.
Can you skip the 2 smithing perks? Possibly. You'll need to compensate by raising smithing skill (much) higher, but if you're already choosing enchanting perks and/or alchemy perks for other reasons...
TLDR:
You can reach 610 armor rating with 9 perks and minor un-perked assistence from alchemy or enchanting. 567 is the armor cap.
Best Answer
There are two things to consider. The first is that Armor Rating in Skyrim has Increasing Returns - that is, the more you have, the better it protects you. So to answer your second question first, the 67 points you're shy of the cap will get you more mitigation than any other 67 points.
It sounds like you should be able to reach the cap with a little bit of Fortify Smithing Gear / Potions.
According to the UESP and my rough calculations, you only need:
67/4 = 16.75/.2 = 84% fortify smithing (This is assuming your smithing is 91 w/ the perk. You need less if you have smithing at 100) which is easily attainable with items / potions.
So with a little investment, you can hit the armor cap with your steel plate.
To answer your first question, once you're at the armor cap, Daedric really isn't better than Steel Plate (unless you like the look) especially because it's heavier.