My Model's Right Hand is Broken, Can Anyone Help? Sadly, my friend here has been in an accident and I do not have the knowledge to fix 'em...

But in all seriousness, what did I do wrong?
I made this model, tried to use a premade rig, and ran into some problems. I think I fixed most of them, and now I found this. For some reason, when I'm in any mode besides edit mode, the right hand goes weird. I have tried looking at weight paint and vertex groups and have found nothing. Can someone please help?
Here is the blend file:
https://filebin.net/4ci3da5fv360m6db
To solve your main problem, in pose mode select the UpperHand.R bone, go to the properties panel, bones tab, Relations tab and uncheck the "Inherit rotation" button.

First you should have your hands locations match the hand bones locations moving in edit mode the bones (or the hands) accordingly.