For question 1, see the comment above.
Collecting the answers to question 2:
- Grothendieck's original FGA, starting with TDTE I
- Vistoli's chapter in FGA explained, for the connection with stacks
- http://mathoverflow.net/questions/22032/what-is-descent-theory for a very short overview
- Bosch-Lütkebohmert-Raynaud, Néron Models (recommended by BCnrd in the above-mentioned thread)
- Waterhouse, Introduction to Affine Group Schemes, containing a 20-page introduction primarily concerned with the affine case
"Community wiki" post, feel free to modify.