You’re asking to have an artificial limiter on your note length. So, let’s say you set the limit at 100 words, then any note you want to compose will be limited to 100 words. But that is an arbitrary number, because a 10-word note can be atomic, but a 10-word note can also not be atomic. The same goes for a 200 word note.
In other words, setting an arbitrarily “low” number does not necessarily achieve your objective of atomicity, AND it is distracting because you’ll be keeping an eye (physically or mentally) on that word counter.
It would be better to revisit the concept of atomicity, and create your atomic notes in a more natural way. You’ll be able to handle your zettel in a better, more satisfying manner, IMHO.