This is a very complicated Kickstarter. In order to simplify it, they have put together some pre-configured kits that come as is. With no Stretch Goals. You can buy Add-ons. Here are the 3 kits.
Here's the link to the Kickstarter. Check it out. Dwarven Forge building pieces are tons of fun. Like Legos for wargamers
Edit. I found some pics on how the modularity of the castle system