I fly this route quite frequently. You are correct that the IAD-SVO is often late. For peace of mind, I usually book the next connecting flight after the one that's most logical as the first one ends up being tight. However, if you do miss a connection, SU is quite good at putting you on the next flight. Just stop at the transfer desk and get your rebooking boarding pass.

If you are on the next SU flight, then your bags will most likely be as well. If they put you on the next AF flight, your bags most of the time show up on the next SU flight at CDG. This is a difference of 2E and 2C at CDG. I still wait in 2E to see if it makes the transfer and if not, I just walk to to 2C and ask the SU ticketing office to give me a pass to the baggage area and wait for my bag to appear. I have never had to have them delivered. For the cost of the ticket, I don't really mind that much.