Sourdough- maintenance question

Your starter will be fine. It'll just be a bit on the sluggish side next time you want to use it, so give it a bit of extra time and patience. Although ideally you'd let it sit for a couple hours before chilling out in the fridge- I've done exactly what you did and things turned out just fine. And yes, if you don't have organic plain flour you can certainly use an ordinary all purpose flour. Just try to make it an unbleached version, if at all possible.