This piece is characterized by a serene, pastoral beauty that reflects Chopin's more hopeful side. It is distinguished by its wide, soaring melodies that make significant demands on the pianist's ability to sing on the keyboard.
The player must maintain a perfect balance of voice leading to ensure the melody never loses its singing quality through the complex passage work.
Comparable difficulty and character — good candidates for what to learn next.
Nocturne in B major, No. 1 is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 8.
You should be comfortable at Henle level 6 — meaning you can already play level 5–6 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 Nocturne in B major, No. 1 lasts about 5.5 minutes.
Nocturne in B major, No. 1 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 Allegretto and Mazurka by Frédéric Chopin, Nocturne in E-flat major, No. 2 by Frédéric Chopin, Nocturne in C-sharp minor by Frédéric Chopin — see the full similar-pieces list on this page.