There were fewer slaves than that in Kansas I believe, but that didn't stop slave supporters from trying to bring it into the Union as slave state. Why should we believe they wouldn't have tried elsewhere?
Why would they want Kansas as a slave state when it wouldn't have any significant number of slaves in it? Could it be that their desire to do so had nothing to do with actually having slaves in Kansas, and everything to do with securing more voting power in Congress?
And yes, they would have tried to get every new state admitted to be a "slave" state so that the would vote as a block against the larger north eastern power block that was then running everything.
Holding the numbers in congress is the only way you can protect your pocket book, and that's still true today.