Hi Jan
I wouldn't worry too much about the smog situation as it's quite a while until you go. I'm sure the authorities will have dealt with the problem by then.
The currency to use is Russian roubles. Bear in mind you might struggle to change them back into pounds in the UK, so either change your money at the airport before you fly home or don't change too much and spend any last roubles at the airport before you come back.
I would recommend visiting the Moscow underground - it's one of the most beautiful in the world, with many chandeliers and ornate tiles.
Kind regards,
Olly, your editor