The cage you’re describing is a little smaller than recommended for one budgie. It’s not the worst, but since you don’t have a bird yet, I’d just go ahead and buy an ideal cage. This cage can be used as a temporary one, such as a hospital or spare cage.
The best thing you can do right now, is to take advantage of the educational resources we have here on the site. By reading all the Stickies posted at the top section of each sub-forum, it will give you a good idea of how to prepare for and keep a new budgie. You’ll find answers to many questions you may have. Also, we’re here to help, so if you can’t find an answer, just ask