There is enough yeast to propagate 5gal, if you wanted to. I culture yeast on slants and build up my starters from, literally, 100 yeast cells. So you would probably want to start with a small amount of wort, maybe 100ml sterile wort. Once you see activity, around 12-24 hours, you transfer to 400ml of sterile wort. From here you can step up to 1L. The key is having sterile wort (pressure cooker), and not stepping the volume up by more than 4x the original volume, you can go from 10ml to 40ml, but 10ml to 80ml would be pushing it. It's best to transfer the yeast when it is active, this ensures a healthy, energetic yeast starter. You might want to perform any transfers over a flame source to ensure no foreign bacteria infects the starter.