The movies show the Rebels being rag tag until RotJ. I don't think they did have significant resources until then. The crawl in IV says they've just won their first battle. The crawl in V more or less says they are on the run and in hiding. It's only when we see in RotJ that they've got an actual expeditionary full spectrum fleet. They clearly weren't waging offensive war and trying to seize ground militarily. RotJ they were waiting for the money shot and to take down the Emperor.
I'm sure they did just steal a lot of what they needed. Whether it was credits or old Clone War era military equipment.