Short stories can sell, but most of them are lumped in the erotica category and/or are serials. Novellas are a better bet if you want short works to sell. However, since you've written some, you should give it a good shot. Not the end of the world, but you should consider slightly longer works (15k+) if you want a better shot in selling shorter works. It goes without saying that shorter pieces of work and their ability to sell depends on the genre, and the market that will want to buy them.
You can leave 1, mainly the first of a series, free as a choice to promote. If you're a beginner + selling short works, KU is something to consider as well - gives you a bit more of an edge on Amazon, but forces you to be exclusive with them. It is a boon also because of the fact that short stories are generally priced (unless erotica, or bundles) at the 99 cents category, and KU at this present time can net you far more than the 35 cents royalty.
If you look around the web, or search around here, there are lists of free promotions specifically for short works that you should utilize because, hey, they're free to use.
Good Luck!