for romantics:
Andante spinato and grande polonaise for romantic pièce. But it is rather long.
The 2nd ballade by chopin is around 7 minutes and about as hard as fantasie impromptu.
Brahms raphsody op 79 no 2 in g minor is really nice and only about 6-7 minutes
liszt ballade no 1 in D flat. i personally like this but some dont so, have a listen
Hungarian rhapsodies boy list id suggest 2,6,10 and 11
id stick with thé sonata cause honestly all sonatas are thé same in thé end
For thé éther contrasting work you could go for impressionistic like
debussy as you suggested. I think Ravel would be nice too.
thé le tombeau de couperin suite is good. i dont know what standard of playing you need though but i would assume it to be RCM ARCT level (im in canada) so thé toccata in that suite should be good
Une barque sur l'océan and aborada del grazioso. I LOVE thèse works. Ive learned The boat on thé océan already and am doing that for my ARCT exam on thé 18th of this month and vie started learning aborada. They are a bit hard though so id watch out
Griffes also wrote some nice works. I like his roman sketches.
a réal weird pièce would be Goodbye Mr Rachmaninoff by katsariss ( i think thats how you spell his name) its short and showoffy-ish
if your looking for more 20th Century stuff thé prokovfiev sonates no 1, and 3 i personally like.
Prokovfiev étude no 1 is quite substantial.
You could go for messine reflet dans vents.
theres also mozetich thé three pièces for piano i dont know thé détail of its name but i had thé score somewhere and those are nice pièces
THere are MANYYYYYYY other works out there so dont limait your self. Just go on youtube and search up random music.
best of luck on your choices and whatever you decide to learn