Do you think I would be able to use the 5 gallon containers in my kit? Or does the containers have to close to the size of the brew?
Can you? Yes. Should you? Debatable. The exact effects of headspace on fermentation are beyond my expertise. Some brewers do open fermentation (effectively infinite headspace); others go to great pains to minimize even the slightest oxygen exposure.
If you want a small fermentation vessel on the cheap, buy a gallon of apple juice in a glass bottle -- minimal headspace and low oxygen permeability. (But hard to clean.) Or some hardware stores sell 2 gallon food safe plastic buckets. (Easier to clean but more oxygen permeable.) Drill a hole in the lid, add a grommet, stick in your airlock.
I'm pretty to new this hobby, too. And when I was first starting, I jumped straight into a 15-gallon kettle and 7.5 gallon fermenter. Both of which have been idle since last July. My idea is that as a new breweer, what I need to do more than anything is just practice, practice, practice. And doing smaller batches lets me do more batches, more often, with lower ingredient costs.