The first story I ever submitted will be published next the spring by an online magazine for no money. Does this limit the possibilities of publishing it elsewhere?
Congratulations! It depends on your agreement with the magazine. In this instance, I would strongly encourage you to confirm that you are only granting this magazine the right to publish your piece nonexclusively and that you will retain copyright to the work. Keep in mind that it is good practice (and good karma) to acknowledge where a piece has first been published; your early supporters will stand by you for your whole career if you let them. I would also urge you only to submit to magazines in which you would be thrilled to publish.