Excellent build you have, that is my first character as well.
Summons work great (you only summon if someone notices you and you can't fire a shot off before they reach you). I personally felt the bound weapon conjuration perks were a waste. This is even more obvious after you raise enchanting.
I use a Daedric bow (enhanced with smithing), and dual enchants of fiery enchant(soul trap + small fire dmg) and I think paralyze if I recall correctly.
I'd much rather have those 2 perks back that I wasted on the bound weapons. Since the enhanced bound bow is nothing compared to a moderately smithed daedric bow. And then the fiery enchant at 1 second is a perfect enchant. Plus you can add another enchant once you get 100 enchanting(not add after the fact, but make another bow and add both).
I maxed Smithing and Enchanting, and was working on Alchemy. I personally think all my characters will max all 3 of those. Enchanting is nearly game breaking, and smithing makes you create ridiculous damage/armor. Alchemy is arguably as good as smith, but due to enchanting being so much more powerful than either, it doesn't matter as much.
Not to mention that I actually fully regret ALL conjuration perks. I still summon if the enemy(ies) are coming at me, but they are there to distract long enough for a shot, not damage. So having multiple (or more powerful) is a waste.
I was wondering if by attacking bare handed, you increase your 1-hand (or 2-hands) weapon skill mastery.
I played through the start of the game unarmed (Khajit), and never increased my one-handed or two-handed skills.
[...]do the Khajiits's +15 claw bonus mean that every one-hand weapon below damage 15 is useless?
If only comparing pure damage, yes.
Does, as example "Backstab" skill bonus apply just to any 1-hand weapons, or to barehand too?
The sneak perk Backstab applies to one-handed weapons, which bare-handed is not.
Can I, say, do a stealthy istant kill from behind when unarmed? Like breaking the neck maybe?
You can sneak attack while unarmed (and with a two-handed weapon) for extra damage. If you do enough damage to kill the opponent in one shot, you may be treated to a special animation. IIRC, there's an unarmed neck snap one.
Best Answer
There is no strength in Skyrim. Increasing your skill with a weapon type will make your attacks with weapons of that type stronger, while buying some perks will make your attacks stronger or give you some new abilities (bleeding wounds with axes, bypassing armor with maces, beheading, etc).