Item 'sold' 10 days ago, invoice sent, buyer not paid or been in touch. Shall I just go for a second chance offer?

[Meglet]

If I select 'second chance offer' does that mean the person who won the item first time (but has not paid) can't leave me any feedback?

Is 'second chance offer' just a normal straighforward sale if the next person wants the item?

No you need to cancel the transaction by opening a "non-paying bidder" dispute and do it that way.