Either I forgot to correct it, or you may have missed it (Which is pretty easy) but you get shade equal to your Charisma score, so up to 20.
Yes, it lets you see through magical darkness. It's like that one Eldritch Invocation. Uhhh, iunno how dispel magic interacts with class features. Antimagic field...maybe?
10 if you blow your whole shade pool. Potentially more if you use the level 15 feature. Uh, probably a Con save. I might leave off the smite bit, then. You're probably right. Though you would be blowing a smite just to guarantee the effect, more or less. The save would be...1d12+5? If you're using a greatsword? And you have to leave the sword there.
Yes. Allies who already have darkvision at or beyond the stated ranged gain the ability to see through magical darkness up to the stated range.
Think about it, though. You can see fully across the barrier. You can use it to bypass and scout anything and anywhere that isn't also defended from the Shadow side. You can have your party pop up right next to the king, then pop out again. You could escape certain death by just hanging out in the Plane of Shadow (Though it, of course, has its own hazards...).
There is the Shade-refresh, though. I imagine that would get used all the time.
Thank . Remember though, you're supposed to make everyone less afraid of the dark, and you're not allowed to spook your enemies with it! What do you think about the spells?