Hello, I actually think Op. 25 No. 1 is fairly doable if you can get the technique down. It's not like some of the other Etudes that require months and months of slow practice to feel comfortable with; it and Op. 10 No. 6 are both pretty accessible. As far as Nocturnes, while I love Op. 27 No. 1, I also recommend you take a look at Op. 37 No. 1 and Op. 15 No. 3. These are still extremely gorgeous pieces, but with a little less immediate challenge than the Op. 27. Also, if you haven't played the opus-posthumous C# minor Nocturne, I highly suggest you check it out!