This miniature is a quintessential example of Chopin's ability to convey profound emotion in a very brief space. Its harmonic structure creates a sense of endless yearning and deep, quiet sadness.
The primary focus should be the seamless connection of chords and the maintenance of a long, singing vocal line in the right hand.
Comparable difficulty and character — good candidates for what to learn next.
Prelude in E minor, No. 4 is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Prelude in E minor, No. 4 lasts about 2 minutes.
Prelude in E minor, No. 4 is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Waltz in C-sharp minor, No. 2 by Frédéric Chopin, Waltz in A minor by Frédéric Chopin, Allegretto and Mazurka by Frédéric Chopin — see the full similar-pieces list on this page.