The link to the template for ISRR papers seems to only have book-like templates, is this the correct one?
The format should the Springer STAR series. It's indeed the book where ISRR proceedings are published. A sample LaTeX template is available here. Otherwise, please use the template available on Springer website ("contributed books" template).
The deadline for submissions has been extended to April 27. do I need to submit a summary/preliminary paper before the deadline?
There is just one date for the submissions: April 27, 2015. you don't need to submit any preliminary version of the paper.