Getting a secondary carboy

I have brewed 3 batches so far using just one 5 gallon carboy. One thing I have noticed with my first batches is that I have only succeeded in getting two full cases from one of my batches. The first one I just didn't fill the carboy quite high enough. Batch 2 I filled more and got almost exactly 48 bottles. This most recent one I filled like #2, but my fermentation was so vigorous that a lot of beer went out the blow-off tube. If I get a second carboy would it be a good idea to get a 6.5 gallon and use it as my primary?

A 6.5 gallon primary is a very good investment. We all hate wasting homebrew!

Yes, do the primary in the 6.5 gal. carboy and transfer to secondary in the 5 gal. Fill the 6.5 to 5.5 gallons that way you'll have a full 5 gal. in your secondary.

I agree with all the other comments. You need to get 6.5 gal carboys.

Save you 5 gal ones for wines, meads, or half batches.

For a 1/2 batch you can brew and mix as usual then transfer 1/2 of the wort to the other 5 gal carboy and use a different yeast. You'll end up with 2 different beers.

Is there a benefit to having some of the kraeusen blow out of the fermenter?

I read, that some of the bitter resins and fusel alcohols are discarded through this process which may result in a better beer. When using a 6.5 gal carboy, this may not be possible anymore.

Under optimum conditions you actually would remove all the kreusen.

Most of us just allow it to fall out.