I leave feeddback as soon as I receive payment ... it has never been a problem or caused any hassles.    At that stage the feedback states that the payment has been received and a thank you.

Any problems later can be sorted out between the buyer and myself (if item isn't received, etc) or through eBay.

Like saarzi, I would leave follow up feedback if a problem arises .... and Yes, in the case of non-payment,  you can always say that payment wasn't received or no contact, "in the nicest possible way" 🙂      There has to be some way to warn others, and that's the only way I know how.