B) what currency (including BTC) is the cheapest/fastest/most secure/simple for international transfers?
my question is a combination of these two questions.
think of it as having someone abroad (like your son in a university in another country) wanting to send him money but do it via bitcoin.
is there a way to reduce the costs and make this as efficient as possible?
What costs are you trying to prevent or reduce? transaction fees are like $4 tops. I think that's cheap enough to send £20k. The only downside of this is you need to teach him how to sell the bitcoins via the GDAX, since I think that's the exchange that Coinbase uses.