Evaluation:
There's a lot to like here, even though it's "conservative" you've added quite a lot of subtlety to the track. The original is basically solo acoustic guitar after all! Love the style, and you know I'm a sucker for the choir.
All of the added strings carry some very emotive work. Their new countermelodies you have added is the highlight for me. IE (1:06-1:26) is heart-wrenchingly beautiful.
After the opening ends, we are introduced to a new element; choir! This is where the majority of the problems lie for me. The attack on the samples is lagging just so slightly behind the beat and it's very noticeable especially when laid next to the piano as it is. I'd suggest to try a couple things: try getting more of an accent whenever there's a reticulation of a note or move up what's there currently to line up with the piano better. The other aspect of the choir is that it sounds like it's in a different space than the other parts. The choir is pushed back in the space and the piano and strings are much closer to the front.
Definitely address the humanization as you mentioned as well, can't forget that.
If you want to take it to the next level, my idea would be to bring back the cello towards the end playing some more lyrical and interesting countermelody to add to the choir.