Translation:When we were opening our first shop, we were poor.
The English translations sounds a little odd. I think most people would probably say - When we opened our first shop we were poor
I believe the verb used in this sentence -- otevírat -- is imprefective, denoting an "in progress" or repeated action, so it is translated as "were opening." The perfective verb, indicating a completed action is "otevřít," which indeed would be translated as "opened."
It sounds ok to me. The speaker is emphasizing that the opening took some time.