Don't ever stop in a piece, it ruins the continuity... it's like, if you were to go to a play, and they messed up a line, and they cut back to an earlier part of the scene instead of just dealing with the mistake.
The waltz and nocturnes are both definitely good choices, though they're both quite commonly played. The waltz will introduce you to his style of well, waltzes, and the nocturne, not counting the things apparent in this one (bel canto, rubato, phrasing, ornamentation, etc), you'll have large groups of notes over 4 or so. This is actually quite a challenge, so I'd actually recommend you take the waltz. But, it's up to you ultimately- get the scores for both (preferably in an actual book, rather than printed off the internet) and play through them, see how you do. For an introduction to the concept of several notes over a few, try the mazurka in A minor Op 17/4(in fact, get the entire collection of mazurkas, it's well worth it IMO), and good sight reading material). It has groups of five notes over one, so still divisible, but IMO it's better to start with that before going into unmeasurable groups.