I think the 'Show notes...' bit you click to open the caption is unnecessary as it's another step you have to take to complete your task (I used to work as a User Experience Designer). Also I feel the same way about the 'Edit in library' because it looks the same as the previous screen.
I went to go and add a 'Label' thinking I was adding hashtags to the post, turns out I wasn't, I was a bit confused at that point.
I mostly use Later on desktop and I am unable to add emoji's until I post and I'm taken to my mobile. It would be cool if you could add emoji's to posts as it's a bit annoying having to add them later as the whole point is to be organised before the post.
I hope this helped! When I worked as a UX Designer I appreciated valuable in detail feedback such as this.