Or if you'd rather not take the chance of problems happening during launch. You could go here the day before, sign in and redeem the code then. Just in case of network problems that sometimes happen during launches.
Yes, but if you plan on getting a vita you mght want to activate it now so you can start to stock up on the games on psn+
Especially since they'll be taking down Gravity Rush, Uncharted: GA, and Wipeout in the coming months to replace them. You could just wait until they announce this at the beginning of October or November (if you are NA subscriber) and then activate and download them before they change over. Then you'll have those games also.