Every battalion is cumulative. Also, I would not base all your information off of scrollbuilder.com. It doesn't make clear what the restrictions on game sizes are, or what units are general battle line and which are specific for allegiance.
All points for all units are in the Generals Handbook, and the matched play missions are very well balanced. The book is fairly cheap. If you're going to play Age of Sigmar, I highly encourage buying the book.
All the unit warscrolls are available for free on the GW website, or in the Age of Sigmar App.
You'll need the battletomes for the specific rules for battalions. The battletomes are not too expensive either. The Sylveneth book, and all books released afterwards are full of all the good allegence abilities and spells and such, which are unique to that faction.
Wargroves are a special king of battalion, which require you to take specific warscroll battalions as compulsory and axillary to field them. You pay points for each Battalion yo take, but every battalion you take, gives you some fun rules and an extra artifact for free.