In our original plan, we had 13. However, we are looking to merge the last two or three chapters into one long chapter. So it will likely be ten or eleven in total. Two of these chapters will contain "character side paths" rather than continuing the main story, though 
Yes, you can start a game in Realm 3, which will give you default choices from Realms 1 and 2. We plan to add an immersive recap to Realm 3 eventually, but right now, if you start at Realm 3, if you are playing for the story, you will miss a lot of key information. However, you can start there if you want to.