(1) As a buyer, I leave feedback after I receive the item and like it.
As a seller, I leave feedback after the buyer leaves positive feedback. In brief (and lets just discuss positive feedback), feedback is to indicate how you liked the other party's role in the transaction. I think it is imprudent for the seller to leave feedback automatically right after he is paid. What's the big deal in paying? The important thing is that the buyer isn't a jerk by complaining (unnecessarily) after he receives the goods -- for examples, lying that he didn't receive it, lying that it is broken, unreasonably complaining about the condition, returning it, threatening you with bad feedback if you don't give a partial refund, etc., etc. If the buyer leaves you positive feedback, you know he is honest and reasonable, so then you leave feedback for him. (Incidentally, since the seller can't retaliate and leave negative feedback for the buyer, it doesn't really matter when and how the seller leaves feedback!)

(2) Unless they did something special for you, buyers and sellers generally don't bother to email the other about receiving and liking the item.As a seller, I put a little form note inside saying I hope they like the item, and give my web site address.

Robert