Anyhow, I'd quite like to allow both an active and reactive attack with the spines.
For the speed, the slower Swim 9 seems more appropriate, although I am wondering about having it have a reduced swim speed when its "puffed out".
Statwise, I'm thinking the Clownfish conversion we did is a good start:
Giant Clownfish: Str 9, Dex 12, Con 14, Int 1, Wis 11, Cha 10
Maybe cut the Dex a step, since it doesn't seem that agile?
Giant Porcupine Fish: Str 9, Dex 10, Con 14, Int 1, Wis 11, Cha 10