We don't know when there will be an iOS7, nor do we know what it'll contain. I do think it's safe to guess if iOS6 didn't contain Siri for the 2 and touch 4 than 7 won't add it. Apple has never said, but current popular opinion is that those models simply lack hardware to make the software work. ANd since you can't update the hardware on an iDevice I personally think Siri is only for future devices.
As to your imessage or facetime question, maybe someone else can address that.
How to Block Someone on FaceTime
You could also get a new email address - gmail? - that you just use for FaceTime and Messages. Give the new email address only to the persons you will FaceTime with.