As far as I understand it, the only thing that matters for enchanting is the level of creature or human you soul trap. So it doesn't matter if you use a human soul or a creature soul.
However, nearly all soul gems only trap creature souls: only black soul gems will trap human souls. And black soul gems are pretty rare. Black soul gems (including the Black Star) work on humans of any level, including common NPCs like bandits. So if you're looking to expand your soul trapping opportunities, having Nelacar repair it is prudent.
However, siding with Nelacar will prevent Aranea from ever becoming a follower, which might not be what you want. While it's stated to only hold Black Souls (Humanoids) it can actually hold all types of souls, making it a straight up upgrade, as long as you're willing to go that way in the quest line.
In terms of a quest to collect all the Daedric artifacts, I'm not aware of any in game. However, if you're an achievement collector, all three platforms have:
Oblivion Walker
Collect 15 Daedric Artifacts
But both versions of the Azura's Star count for it, so choose whatever you want.
And as an aside, there is an Oghma Infinium quest, just not in the same style as Oblivion:
The reward for the quest Discerning the Transmundane is the Oghma Infinium, one of the 15 Daedric artifacts.
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.
Best Answer
You can purchase Armored Trolls relatively early if you side with the Dawnguard's quest line. Also, you can recruit a new added in dog breed similar to a husky.