I have heard that using too large of a fermentor can lead to issues with oxidation and infection due to the large head space in the container.
This is only a concern if you leave the beer with a large headspace for an extended time once it has finished actively fermenting. If you can rack it to a secondary vessel that is close to the finished volume, such as a one gallon glass jug, that would be fine. Such a jug is too small for primary because it doesn't leave enough headspace.
If you prefer the ease of avoiding secondary and bottling straight from the primary, then I'd find a 2 gallon white plastic bucket at Home Depot.
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