Looks great I love begonia Rex my favorite terrarium plant.
What’s the dimensions on that?
I think you have a perineal hibiscus they wilt during the winter try a red darling they bloom huge flowers year round (pic below).
You can replace it with orchards they do well in terrariums imo.
It's 2x2x4 feet. I have a Begonia on the bottom and a white moth orchid at the top. They are in my picture. =)