No, the reward can be used to halve the avios for a solo trip now not just for a couple travelling. It's much more useful.
Yes and Yes. But wait until the voucher is in your BAEC account. Once there it won't disappear until it expires or is used.
Most people believe you can use *any* Amex card to book the reward, not just the BA Amex (Black or Blue). But the phone agents often get it wrong.