What did you make exactly? I don't know much about wine, but I would follow commercial storage conventions for the style you made. I think storage temperatures should be lowish unless the style specifically says otherwise, but I'm hesitant to mention a number. 50s-60s would make me more comfortable than 30s-40s or 70s-80s I think.
Some general tips about avoiding oxygen contact include never pour until it's about to go into your mouth, don't splash, and, since you're doing wine, perhaps you should cork it? If you plan long-term storage, perhaps just store it in a glass carboy with an airlock. I've seen that work with mead for 2+ years, but grape wine may be different. CO2 is a heavy gas, so it should act as a buffer, as you say, and this would work better if the temperature stays stable.
Introducing controlled CO2 could help if oxygen exposure is really a problem. I think the Blichmann Beer gun has a feature that lets you fill a bottle with CO2 before you fill it with beer; maybe you can adapt that to wine? For really long-term storage, once fermentation is complete, a keg with a bed of CO2 on top of the wine might help. I think you probably need to pressurize to 5 PSI or so to keep a seal, which might result in a slight carbonation. Basically you would fill the keg, pump CO2 in, purge, and then do it again without purging. There are small kegs you can buy.
Check your sanitation regimen. Bottles should be clean and sanitized, no visible residue or scratches and should be exposed to a light sanitary solution or baked immediately before filling.
Finally, avoid contact with light. Cellars are used for alcohol storage because they're dark, dry, and cool!