This early on, you're fine. The concern with oxygen is that it feeds acetobacter, once it gets going, which will create more acetic acid than you want... acetic acid = vinegar. Plastic buckets work, but can allow in more O2 than is desirable over a long aging period, which is something you want to be aware of. The Mad Fermentationist, I believe, prefers plastic carboys (Better Bottles, etc).
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