1. Russian legislation dictates that they won't even issue boarding passes from a different airport (on separate bookings) even if they are on the same day, as I've found out, so I wouldn't be surprised if they wouldn't do this (bureaucracy)

2. arriving domestically in SVO, you just walk out, that's it. I have no idea what domestic > international transfer is like but the transfer desk should be able to point you into the right direction, but please do be aware of which terminal you arrive into - the newly opened Terminal B is a little bit far from Terminals D-E-F (but connected by free transfer)

3. I've only ever had one delay flying within Russia, which was 5 hours late at night and due to a snowstorm that just started. If anything, I've landed everywhere early! Not to mention LED-SVO is extremely frequent.

If you go by train from St P to Moscow, you'll arrive in Leningradsky (Oktyabrskaya on train tickets) vokzal (rail terminal), the Aeroexpress to SVO departs from Belorussky which departs on the hour and half hour. They're connected by the brown circle line on the metro, 10 minutes travel time (but bear in mind the several minutes you need to get from surface to platform and vice versa! (Moscow metro stations are VERY deep)

Trains are pretty punctual, although bear in mind they also have airport-style security in every major train station, the Sapsan takes 3.5-4 hours depending on which one you take - https://pass.rzd.ru/tickets/public/e...0&checkSeats=1