i'd say the 2nd story starts around chapter 47, and no they're not really connected so you could probably start from 47 and still get the gist of what's happening. i'd still recommend reading from the start cause the first story is good, and you'll get a full understanding of what's going on.
From which chap does the 2nd story start? Also is it okay if I start from the 2rd story? Are they connected in some way?