I think op. 90 is somewhere between moonlight and Tempest in terms of difficulty but it completely depends. Some People thinks it is as hard as Appasionata and some think it is one of the easiest. I think it is in the middle. But if you han do op. 90 justice you can probably do the Images. But that also depends on which your strenghts are. So I think the best one to say how difficult these pieces are is yourself, because I am sure my opinion is very different to your opinion. Hope I could help!
Thanks! Well, I would actually truly appreciate suggestions on new repertoire to play! I have played earlier pieces like Beethoven Op 90, Op 26 and Op 13 (all complete), Schubert complete op 90 and his b-flat impromptu D 935 no 3, Chopin's Op 10 3 and 5, and his Op 37 no 2 and Op 48 no 1, Brahms Op 118 2, Bach's Italian Concerto(all mvts) and P&F in e minor bk 1 and E major bk 2. And also Mozart K 282, Rach's Op 32 10 in b minor and Debussy's complete Estampes. So if you have suggestion for new repertoire which is a Nice next step in difficulty really appreciate it!:)
Also, which piece is harder according to you between Rachmaninoff Op 23 5 and Op 32 10?