Hi, Bbockelmann! Welcome to the Gotmead community!! You've come to the right place for help with your first batches!
But, before I answer your questions, I'd like to suggest that you read the Newbee Guide (there's a link over on the left side of this page), so you can understand why we suggest some of the things that we do.
Now to your questions. First, Joe's recipe is scaled for a single gallon batch, but if all you have are 3 or 5 gallon carboys, you can certainly scale up the recipe (multiply everything by either 3 or 5) and it will work just fine. It is better to keep the airspace above your mead as small as possible, especially after fermentation is finished and your mead is aging. That will prevent oxidation.
As far as the Better Bottles are concerned, I still use glass, but that's mostly because I've been doing this for a while and I have enough glass carboys to do most of what I have planned. If I were buying new equipment I might add some Better Bottles to the collection since they are cheaper, more robust against breakage, and the like. From what I've read, they should be as good for primary or secondary fermentation as glass vessels. I don't know if I would try any really long-term aging in them. I'll let those folks with experience using them answer that more definitively.
Don't be nervous -- mead is a mostly forgiving mistress. Just take care to keep up good cleanliness and sanitation practices, and follow directions, and your mead will likely turn out fine! Good luck with it!!