Wow, what are the chances that your B would contact you when that's all that's been discussed on your new thread! Timing is very cosmic!
Well, now that he mailed you something.. I personally think it wouldn't be out of the question to mail him something in return.. but I have to say I don't really think that an email is necessarily impersonal.. it was a good way to reach out in a non-threatening or non-pressuring way.. But as I said, he has paved the way by way of the postal service..
I thought the underwear idea was very cute/funny.. but I'm kind of a quick wit and a little sarcastic person so I'm not sure that I'm a very good judge on if it's the right choice!