batch sizes and usable equipment

so I have been seeing some threads about 1 gallon batch sizes. I was thinking about doing a small batch for my wife and her friend (raspberry wheat) rather than do a 5-6 gallon batch. So far I have only done extract (no boil) kits till I get more comfortable. Since the Mr. Beer refills make 2-1/2 gallons can I use one of those refills in my 6 gallon fermenting bucket with no problems? I didn't know if the amount of airspace would make a difference with fermentation.

Yep it will be fine. I've got two 5gal buckets with about 2.5gal in them right now. Just don't expect to see as much action in the airlock.