Your assumptions are correct, based on what I know and the numbers you provided. I'm not sure how you calculated how big the dictionary would be (file size wise) but that seems like too big a number.
Essentially, if you use something like this for the passphrase:
With a unique (as in not in a dictionary somewhere) SSID, no one will break it. Period.
Of course, then you would just go and install a keylogger and not worry about breaking it