There isn't any need to darken the room or cover the cage while your dragon brumates. Switching out the MVB for a regular bulb during the time your dragon sleeps is fine though. I just use the strip lights myself as my cages are not high enough to use them safely.
One thing you can do is weigh your dragon. While brumating they should not lose much weight, under 10% through their entire brumate. If they are losing more then there is some underlying health issue going on.
As for the calcium, I recommend using the calcium with D3, but only once or twice a week. If your dragon eats all her greens, extra calcium isn't needed as much with adults, unless she is laying eggs (fertile or infertile) as this depletes their calcium stores quite a bit.
-----
PHLdyPayne