1. the "pure blood" comment probably refers to shinigami who have atleast one shinigami parent compared to those who die and then become shinigami.

2. the "best friend" remark wasn't from the manga, so that can't really be taken as 'true'. Though its obvious that isshin and urahara know each other, possibly from SS.

3. To the manga readers: in the manga, didn't isshin cut grand fisher in half vertically instead of cutting open his stomach like he did in this ep?