The right amount. The right way.

Enough that you're comfortable, which matters more than any average. Customs vary considerably between countries and families, and what's generous in one place is modest in another – so the plan gives a range for your situation rather than a figure. A smaller amount given thoughtfully is a proper gift; stretching beyond what you can afford because someone else gave more is not something anyone would want from you.

Yes, provided the reasoning is consistent and you can explain it. Scaling by age works well, and children accept it easily when it's framed as something that happens to everyone in turn. The alternative is the same amount for all with the presentation varied by age. Both are fine; what causes trouble is amounts that vary with no pattern anyone can see.

Two things do most of the work, and neither costs anything. Present it as something rather than hand it over – folded, hidden, wrapped, part of a small hunt. And write a card that refers to them specifically: a plan they mentioned, something they're saving towards, what you hope the year brings. The money is the same; the difference is whether there was any thought behind it.

It sits badly as a sympathy gift, as a thank you to a host, and to a manager or anyone senior to you at work, where it reads as transactional. Between partners it depends entirely on the couple. A reasonable test: if handing the notes over face to face would feel awkward, choose something else – a contribution towards something specific usually works better.

For adults and anyone comfortable with it, yes, particularly at a distance – add a proper message rather than leaving the payment bare. For children, older relatives and formal occasions, something physical still lands better. A good compromise is a card with a small amount inside and the rest transferred: the card makes the moment, the transfer carries the amount.