I am also very new to home roasting coffee but have taken your exact question to heart. I am using vacuvin brand stoppers and pump with brown glass beer bottles. Though the internet is apt to discredit the vacuvin system as not pulling enough of a vacuum to actually prevent oxidation
in wines, I imagine, as you have, that by removinging as much of the oxygen-rich air as possible and then allowing the beans to refill the bottle with CO2, some preservative effect must be gained. However, as for the vacuvin stopper acting as a CO2 release valve, I have my doubts. I took the stopper and put the end that goes into the bottle in my mouth, blowing out as I imagine the CO2 would do from within the bottle. I found that quite a bit of pressure is required for air to pass outward through the stopper, much more than I imagine the CO2 creates within the bottle. This is likely the biggest drawback of this proposed method. The bag and tin-style valves are very passive devices (allowing air pressure to equalize between the inside of the bag or tin and the outside world) while the vacuvin system is designed (in theory) to actively create and maintain a strong pressure gradient. Thus it is not likely well suited to allowing freshly roasted beans to off gas. However, after the initial CO2 release (first three days or so?), it may be a useful means of preserving beans mid-to-long term (as others in this thread have said.) For now I am using a tin like the one available in the SM store for freshly roasted beans and then the vacuvin for storing beans I will not brew within a week. Thoughts?