that hissing is normal when you install an open-style filter such as on an SRI or CAI .... surprised nobody told you that yet, its not an air leak it comes from the filter itself (mine does it, and so does everyone elses)
it should go away once the cars been running for a bit, thats how you know its not a vacuum leak or anything ... so dont worry
and as far as the IAT sensor, as long as you dont have problems with the car i wouldnt worry about it - but it should be dangling somewhere off the right of the engine bay along the inner fender