I brewed beer for about 15 years, did cider a few times along the way, so here are some notes.
Flip top bottles will be more expensive, but may be the way to go if you don't want to have to buy a capper and bottle caps. They are usually a little larger as well.
5 gallons is 640 fluid ounces, so you can figure out how many bottles you need with a bit of math if you make a larger batch.
Yeast nutrient is a great idea for ciders, he is using champagne yeast which will eat all the sugar, which if you don't backsweeten at the end will be super dry. Ale yeasts can also work and will impart different flavors.
I always did a blow off tube instead of an airlock to start, if you have a super vigorous batch it can clog your airlock and blow it off. As others have said, there will be a lot of gas production, I wouldn't trust a balloon.
This might be a good time of year to see about getting natural cider if you are in an apple producing area, my homebrew shops always had a hook up.
Sanitization is also key, I loved using Star San, it gets foamy and is easy to dunk bottles, equipment, and other stuff in it (it's sold as a super concentrate). Spray bottles are also great.
IF you have an apple source already (FrenchyD), you need to crush them down to get the juice out. You can rent a crusher at a homebrew shop if you don't have one already. In many cases, you actually don't have to buy yeast either, as the apples should have some already on them, but it may be good to add some commercial as you never know what natural yeast flavors you might get. I'd try a natural and a commercial version myself. Also pectin tablets will help break down cell walls and release more juice, I believe that was mentioned in the video.
You can also add fruit as your sweenener, blackberries and raspberry juice work nicely.