Just a little tip I would add would be putting 4-5 male guppies in the sorority as well, since they will break up any fights, and can help to break sightlines.
Other than that, all of this is great information!
I wanted to start a Sorority of my own, but had little to no knowledge of having one. I have a single male betta so I don't have to think about what issues may occur other than keeping him healthy and happy. This gave me more information than I was expecting and with that I can now use to hopefully start a successful sorority.
There's one thing I can correct on, I know a lot of people and a lot of experts would disagree with the colour thing. I know sometimes. Sometimes. Having different colours helps it work, however I've had people who've had sororities that are all one colour, all one type, and different variations. I have 2 females that are exactly the same, but they've never even had fight compared to what one of them does to the other girls. Just a tip :)
10 gallon doesn't really provide sufficient space as a minimum, I'd say 15 gallons at the bare minimum, but a 20 gallon (both high and long) would be better. Secondly, I'd say an odd number will be better than the even numbers that has been posted above, since the alpha scenario will work out bettter. Otherwise, though, I think that the author was accurate on the parts Introducing and Agression, The Back-up Plan and Feeding, so that would result in 3 stars for me.
I wouldn't recommend a betta sorority to a beginner. Also in my opinion twenty gallon, heavily planted tank with at least seven female bettas is the bare minimum for a betta sorority. They need that extra room for territory, and seven bettas will disperse the aggression. Four to six bettas in a ten gallon which this article recommends, would most likely end badly. I give this article two stars because of the information of feeding, having a back up plan, and picking out betta paragraphs. Those give good information in my opinion.