Then I would put the opera transcriptions in the second half.
How about 'Ad nos, ad salutarem undam'?
I heard Busoni's Chopin variations over the radio a while ago, part of the Sydney International Piano Competition. Sounds tricky, but most of Busoni would be tricky anyway. Thought I'd mention it.PS I found a youtube clip which has snippets of the piece
Things get crazy about 9:50!